Center Research Brief #10. - Center for Agroecology & Sustainable

12 Pages·2006·1.38 MB·English

The CENTER for AGROECOLOGY & SUSTAINABLE FOOD SYSTEMS
UNIVERSITY OF CALIFORNIA, SANTA CRUZ RESEARCH BRIEF #10, FALL 2006
Food Safety versus Environmental Protection on
the Central California Coast: Exploring the Science
Behind an Apparent Conflict
– Diana Stuart,1 Carol Shennan,2 and Martha Brown3
The September 2006 outbreak of Esch- government, and non-governmental organiza-
erichia coli O157:H7 traced to Salinas tions to address environmental problems in
CENTER
Valley spinach has spotlighted prob- Central Coast counties, and the effectiveness
lems with food safety on Central Coast farms of these measures at reducing pollution. We
•
and in food processing facilities. This is not then summarize the history of food safety
the first time the Central Coast has been in issues and outline potential sources of crop
RESEARCH
the food safety spotlight: nine other E. coli contamination in the field. Finally, we discuss
outbreaks have been traced to lettuce and the ways that food safety guidelines conflict
• leafy greens from the region in the past decade. with environmental protection methods, and
Although it is important to note that 90% of propose the idea that such methods could
BRIEFS pathogenic E. coli contamination events are in fact reduce contamination sources and
traced to meat products (see sidebar, next improve food safety.
page), produce-based outbreaks place enor-
mous pressure on growers to limit or eliminate BACKGROUND
potential sources of contamination from their Encompassing Monterey, San Benito,
farming and processing operations. Santa Cruz, San Mateo, and San Luis Obispo
At the same time, Central Coast growers Counties, the Central Coast is one of the
face regulatory mandates to limit pollution most productive and profitable agricultural
originating from fertilizers, pesticides, and regions in California, providing high-value
erosion sources. Coalitions of growers, specialty crops to consumers nationwide.
government, and non-governmental organiza- Central Coast growers produce over 200 types
tions have worked hard to put in place “best of crops, generating up to five billion dollars
management practices” using non-crop veg- annually. Monterey County’s Salinas Valley,
etation such as filter strips, vegetative barriers, known as the “Salad Bowl” of America, pro-
contour buffer strips, grassed waterways, and duces up to 82,000 tons of lettuce each year.
constructed wetlands designed to minimize the Other specialty crops grown in the region
impacts of agricultural pollutants on adjacent include strawberries, artichokes, broccoli,
waterways and wetlands. and spinach.
This research brief examines the way that Intensive row crop production brings with
pressures on growers to achieve both food it the potential for environmental impacts on
safety and environmental protection are con- natural resources, including streams, rivers,
nected—and may be on a collision course. and wetlands. Working with government
Growers who have recently adopted prac- agencies and non-governmental organiza-
tices to minimize water pollution may now tions, Central Coast growers have responded
face pressure to eliminate these conservation to mandates to reduce the deposition of nutri-
measures in order to meet industry guidelines ents, pesticides, and sediment into waterways
that call for “clean” fields in the name of food and sensitive ecosystems. Specific practices—
safety; such guidelines aim to minimize the most of which use non-crop vegetation to
presence of wildlife, seen as a potential disease absorb and filter out pollutants—have been
vector. This raises the specter of Central Coast designed to reduce impacts of these agricul-
farmers having to remove non-crop vegetation tural pollutants.
for some distance around their fields, greatly Along with environmental challenges, the
increasing potential losses of nutrients, pesti- other, highly visible issue facing Central Coast
cide residues, and sediment, not to mention the growers and food processors is reoccurring
loss of biodiversity and habitat for beneficial problems with food safety. The most recent
insects and birds. outbreak of E. coli 0157:H7 in September
Using information from existing research, 2006 was associated with spinach from the
we explore the question: Are the goals of Salinas Valley. The outbreak led to 3 deaths
environmental protection and food safety and sickened more than 200 people in 25
Research mutually exclusive on the Central Coast, or states and Canada, prompting the removal of
can we have safe food and a healthy environ- both fresh and bagged spinach from grocery
Brief #10
ment? To do so we examine efforts by growers, shelves and restaurant menus nationwide.
1Department of Environmental Studies, UCSC; 2,3Center for Agroecology & Sustainable Food Systems, UCSC
Food Safety and Environmental Protection
Growers have been trying to address water quality issues, but could also ent runoff. Vegetable systems are more
all possible sources of contamination. potentially increase the presence and likely to result in nutrient leaching due
The agricultural industry is already transport of pathogenic bacteria. to frequent cultivation, relatively short
using food safety guidelines created periods of growth, and lower nutrient
by industry groups and third party CENTRAL COAST COMBINES INTENSIVE uptake efficiencies (Di and Cameron
auditors to guide growers in eliminat- FARMING, FRAGILE HABITATS 2002). In addition, the climate in the
ing E. coli 0157:H7 sources from the Water quality problems on the Central Coast can increase the extent
fields. There is increasing pressure to Central Coast stem in part from the of nutrient discharge: accumulated
turn these guidelines into mandatory presence of intensive agriculture in nutrients in the summer and fall are
regulations. an environmentally sensitive setting. washed into waterways during the first
However, various industry guidelines The area juxtaposes fertile soil and a rain events of winter.
currently conflict with environmental climate ideal for year-round cultivation Nutrient run-off can result in exces-
practices by encouraging growers with an extensive network of coastal sive plant and algae growth, leading
to remove any non-crop vegetation waterways and wetlands supporting to eutrophication and degradation
that could attract wildlife, viewed as unique plant and animal communities. in aquatic and marine ecosystems.
possible disease vectors. Non-crop The watersheds of the region, includ- Sedimentation in runoff is especially
vegetation is a key component of ing those of the the Pajaro River, the harmful to threatened and endangered
current strategies to address regional Salinas River, and Elkhorn Slough, Steelhead and Coho Salmon found in
water pollution. empty into the Monterey Bay National the region. In addition, the presence
Before current food safety guide- Marine Sanctuary, the largest marine of pesticides in waterways has been
lines are further adopted or become protected area in the United States. linked to declines in amphibian popu-
mandatory, it is important to evaluate Elkhorn Slough is also one of the larg- lations throughout California, including
their full impact. Removing envi- est remaining tidal wetlands in the US the federally threatened red-legged
ronmental practices would not only (NOAA 1999). Approximately 75% frog found in the Central Coast region
reverse progress towards addressing of the land surrounding these water- (Davidson et al. 2001, Davidson 2004).
sheds is used for agriculture (State of Overall, pollution associated with
Meat Is the Major Culprit in California 1997). agriculture in the region is harmful to
E. coli O157:H7 Outbreaks The waterways entering the marine terrestrial, aquatic, and marine ecosys-
Certain strains of E. coli bacteria sanctuary have repeatedly failed to tems as well as humans if ingested.
normally live in the intestines of cattle, meet water quality standards due to
wildlife and humans causing no harm. significantly elevated levels of nutri- COOPERATIVE EFFORTS ADDRESS
The O157:H7 strain became known in ents, pesticides, and sediment (Caffrey POLLUTION PROBLEMS
1982 as a result of an outbreak associ- et al. 2001, Hunt et al. 1999). Since For the past several decades,
ated with hamburger meat. It causes agriculture in the area is dominated by government and non-governmental or-
severe diarrhea and can lead to kidney vegetable and strawberry production, ganizations on the Central Coast have
damage and even death. Young chil- the region is especially prone to nutri- been working with the agricultural in-
dren and the elderly are particularly
vulnerable. P
a
An estimated 73,480 illnesses ul Z
occur each year in the United States are
due to E. coli O157:H7 resulting in an ts
k
y
estimated 2,170 hospitalizations and
61 deaths (Mead et al. 1999). Most
of these outbreaks are traced to the
consumption of contaminated meat,
which is usually infected during the
slaughtering process.
Consumption of ground beef is the
most common vehicle of food borne
E. coli O157:H7 outbreaks: 41% of food
borne outbreaks are from ground
beef, whereas 21% are from produce
(Rangel et al. 2005). Almost half of all
produce contamination occurs during
food preparation due to cross con-
tamination with contaminated meat Row crop agriculture and grazing operations surround Elkhorn Slough, one of the largest
remaining wetlands in California. Slough waters drain into the Monterey Bay National Marine
or other foods in the kitchen (Rangel
Sanctuary. Due in part to agricultural activities, these waters have repeatedly failed to meet
et al. 2005). water quality standards.
2 CENTER RESEARCH BRIEF #10 | Fall 2006
Center for Agroecology & Sustainable Food Systems
dustry to address water pollution issues. Native grasses Ch
Conservation programs run through planted adjacent ery
the US Department of Agriculture to a water and l L
a
Natural Resource Conservation Service sediment control m
basin located near b
(aNssRisCtaSn)c eo fafenrd teecnhcnoiucraalg aen gdr ofiwnaernsc itaol Ehleklhpo cranp Stulorue gh ert, NR
adopt environmental practices to reduce sediments and CS
pollutants from
erosion and improve water quality and
nearby agricultural
wildlife habitat. These practices in- operations.
clude installing filter strips, vegetative
barriers, contour buffer strips, grassed
waterways, and constructed wetlands
(see sidebar, below). According to the
NRCS, these practices improve water
quality by reducing erosion and remov-
ing organic matter, metals, pesticides,
nutrients, fertilizers, and animal wastes program provides support for states to Thanks to the efforts described
from agricultural run-off. Although the establish their own efforts to address above, growers on the Central Coast
effectiveness of such modifications is NPS pollution. are among the most active in the state
site and design specific, their adoption In California, the State Water in addressing regional environmental
is considered the best way to reduce Resources Control Board and nine Re- problems. Many government and non-
possible environmental degradation gional Water Quality Control Boards governmental organizations now work
from agricultural activities. (RWQCB) administer the NPS program. closely with the agricultural industry to
Pressure on growers to reduce ag- Because agriculture is the leading source protect waterways and biodiversity in
riculturally-related water pollution of NPS pollution in the state, almost the region.
increased in 1987, when Congress all of the program resources focus on The Agriculture Water Quality Alli-
amended the Clean Water Act and es- addressing agricultural pollution. The ance is an example of this cooperative
tablished in section 319 the “Nonpoint Central Coast RWQCB has developed a approach to water quality improve-
Source Management Program,” recog- program that includes grower education ment. Created to protect the Monterey
nizing the need for leadership to address efforts and increasing the use of the same Bay Marine Sanctuary, it encour-
non-point source (NPS) pollution.1 This practices supported by the NRCS. ages growers to promote environmental
stewardship by providing educational
programs, consulting services, and
Vegetation-Based Practices Used to Improve Environmental Quality research efforts. The organization is
Filter strips: Areas of vegetation for removing sediment, pollutants, and or- a partnership amongst the marine
ganic matter from run-off water. This occurs through filtration, deposition, sanctuary, six county Farm Bureaus,
infiltration, and decomposition of materials before they enter effluent water the NRCS, six Resource Conservation
flow. Filter strips are recommended along field edges, waterways, and around Districts (RCDs), and the University of
livestock areas to reduce pollution (NRCS 2006). California Cooperative Extension. More
recently, the Central Coast RWQCB has
Vegetative barriers: Permanent strips of dense vegetation that cross major
been further developing its NPS pro-
flow areas, reducing erosion, managing water flow, and trapping sediment
gram, which requires growers to enroll
(NRCS 2006).
in education programs and watershed
Contour buffer strips: Narrow strips of permanent herbaceous vegetation
monitoring. There are approximately
that reduce erosion, facilitate sedimentation, and reduce the transport of
2,500 growers in the Central Coast
contaminants (NRCS 2006). They can be used within or along the edges of
region, and about 438,000 acres of
fields.
irrigated farmland. According to the
Grassed waterways: Natural or constructed channels with established veg- RWQCB, approximately 800 growers
etation. Grassed waterways are designed to convey runoff, to reduce overall have completed 15 hours of water qual-
erosion, and to improve water quality (NRCS 2006). ity education, and almost all growers
Constructed wetlands: Wetlands designed to treat surface runoff and waste- have at least one management practice
water from livestock operations and agricultural fields. Constructed wetlands in place to reduce runoff and/or water
reduce the concentrations of metals, pesticides, nutrients, fertilizers, and pollution.
animal wastes and also provide wildlife habitat (NRCS 2006).
EFFECTIVENESS OF NON-CROP VEGETATION
IN REDUCING WATER POLLUTION
1 Non-point source pollution is diffuse pollution that cannot be attributed to one specific No single practice can solve the
source. This contrasts with point-source, or “end of pipe” sources of pollution, which problems of diffuse sources of water
have been addressed through US environmental regulations. pollution, therefore certain practices or
CENTER RESEARCH BRIEF #10 | Fall 2006 3
Food Safety and Environmental Protection
combinations of practices may be best been shown to reduce runoff and sedi- FOOD SAFETY A CRITICAL ISSUE ON THE
suited for specific locations depend- ment delivery by up to 97% (Fiener CENTRAL COAST
ing on activities, topography, and the and Auerswald 2003a), and to reduce Since 1995, there have been 20
pollutants present. Using non-crop soil mineral nitrogen content by up to outbreaks of food-borne illness from
vegetation to “bioassimilate” pollut- 84% (Fiener and Aueswald 2003b). E. coli 0157:H7 on lettuce or leafy
ants is held to be the only sustainable, One study found that grassed water- greens; of these outbreaks, nine were
cost-effective, and ecologically sound ways can reduce agrochemicals present traced to the Central Coast. In 1996, a
approach to addressing problems of in runoff water by up to 56% (Brigs significant outbreak of E. coli sickened
diffuse agricultural pollution (Osborne et al. 1999). Vegetation in waterways over sixty people on the East Coast and
and Kovacic 1993). may be especially important for reduc- was linked to lettuce from a San Benito
According to Dabney et al. (2006) ing pesticide concentrations: studies County farm. Contamination of lettuce
vegetative buffers such as filter strips, have shown that a greater retention or spinach from Monterey County was
vegetative barriers, and contour buf- and absorption of pesticides occurs in linked to one major outbreak in 2002
fer strips can retard, retain, and vegetated compared to non-vegetated and two other outbreaks in 2003. An
metabolize pollutants. Buffers restrict waterways (Moore et al. 2002). outbreak of E. coli in Minnesota in
pollution by reducing drift, increasing Constructed wetlands have also the fall of 2005 was also linked to
sedimentation, increasing uptake by been studied for their effectiveness at salad mix grown in Monterey County.
plants, and increasing microbial ac- reducing the release of agricultural Most recently, in September 2006 an
tivity (Locke et al. 2006). Buffers less pollutants. Case studies in the U.S. outbreak of E. coli 0157:H7 affected
than 1 m wide can still trap significant indicate that constructed wetlands can consumers in over 25 states, drawing
amounts of sediment (Van Dijk et al. remove up to 68% of nitrate-nitrogen nationwide attention. Food safety has
1996, Blanco-Canqui et al. 2004). and 43% of phosphorous from agri- become a critical issue to be addressed
Nitrogen can be retained in vegeta- cultural drainage water (Woltemade in the region.
tive buffers through vegetative biomass 2000). Another study shows that There are many possible reasons for
uptake and bacterial denitrification constructed wetlands can reduce total the increased occurrence of food-borne
(Haycock and Pinay 1993). A review phosphorous by up to 41% (Uusi- illness from fresh produce in the past
of major studies investigating veg- Kamppa et al. 2000). Wetlands trap several decades. Whereas produce-
etative buffers indicates that nitrogen sediment and nutrients, although there associated outbreaks accounted for
reduction ranges between 40–100% in may be limits to the amount of nitro- 0.7% of all food-borne outbreaks in
subsurface water and between 73–98% gen and phosphorous they can retain. the 1970s, they accounted for 6%
in surface water. In the Central Coast Microbial actions in wetlands can also in the 1990s (Sicapalasingam et al.
region, nitrogen uptake may best be convert nitrates into harmless nitrogen 2004). This could be related to the
addressed by planting a combination gas (Schaafsma et al. 2000, Hey 2002). overall increase in consumption of
of deep-rooted perennials with winter Efficiency of nutrient trapping depends raw fruits and vegetables (Bureau of
cereals that can take up nitrogen dur- on the rate of flow, the residence time, Census 1996, Beuchat 1996), changes
ing winter rains (Los Huertos 1999). and the vegetation present (Zedler in human demography, microbial
The review mentioned above also 2003). The vegetation in constructed adaptation (Altekruse et al. 1997),
found that phosphorous reduction wetlands may also be important for and/or changes in farming or process-
by vegetative buffers ranges between the attenuation of chemical pesticides ing practices (Beuchat 2002).
50–85% (Osborne and Kovacic 1993). (Milam et al. 2004). Food contamination can take place
Periodically harvesting vegetation can These studies illustrate that envi- at any point between the fields where
also increase phosphorous retention ronmental practices using non-crop food is grown and when food is con-
(Osborne and Kovacic 1993, Uusi- vegetation in buffers, filters, and con- sumed in the home or at a restaurant.
Kamppa et al. 2000). structed wetlands within and adjacent Possible sources of contamination in-
Vegetation can reduce pesticide to agricultural fields can successfully clude improperly composted manures,
release through uptake by plants, reduce levels of agricultural pollutants. irrigation water containing manure
microbial activity in the root zone of The success and efficiency of pollutant or sewage, contact with domestic
plants, extraction of contaminated attenuation is highly dependent on animals, contact with wild animals,
water, and by reducing the movement the specific site and design. As design contaminated wash water, human han-
of water through the soil (Karthikeyan standards are refined, the large-scale dling, contaminated ice during storage,
et al. 2004). Vegetated buffer zones adoption of these practices could or contamination during packaging,
have been found to effectively remove significantly reduce levels of pollution slicing or shredding, and food prepara-
39–71% of pesticides from surface associated with agriculture on the tion (Beuchat and Ryu 1997, Beuchat
runoff, depending on the type of pesti- Central Coast. However, the progress 2006, Tauxe 1997, Francis et al. 1999,
cide (Syversen and Bechman 2004). made introducing and encouraging the Rangel et al. 2005).
Fewer studies have investigated the adoption of these practices could be Most of the outbreaks are due to
effectiveness of grassed waterways. substantially reversed due to conflicts pathogens that have animal reservoirs
However, grassed waterways have with food safety guidelines. or zoonoses, i.e., pathogens that can be
4 CENTER RESEARCH BRIEF #10 | Fall 2006
Center for Agroecology & Sustainable Food Systems
transmitted from animals to humans Ready-to-eat crops such le
(Tauxe 1997). Although there are as spinach and lettuce ila
many different types of bacteria associ- have a greater chance
of causing food-borne
ated with animals, only certain strains
illness because they are
of bacteria are harmful if ingested by
often not cooked.
humans. For example, there are many
types of Escherichia coli (E. coli) bac-
teria found in the intestines and feces
of all animals. However, only specific
types of E. coli, such as Escherichia
coli 0157:H7, cause illness in humans.
Documented outbreaks of E. coli 0157:
H7 have occurred from “ready to eat”
and minimally processed foods such as
apples, cantaloupe, sprouts, spinach,
and lettuce. These foods retain a large mile from the spinach fields (Bridges grain to cattle has become a common
portion of their original microflora 2006). practice, manure may now have higher
accumulated during growth (Francis et Both raw and composted cattle concentrations of pathogenic bacteria
al. 1999). Because these types of pro- manure are often applied as a fertility than occurred with traditional feeding
duce are often not cooked, they have source in farming systems, although regimes. These researchers conclude
a greater chance of causing food-borne the use of raw manure has been modi- that feeding cattle hay could reduce
illness if contaminated with pathogenic fied in the Central Coast region (see pathogen excretion and lower the levels
bacteria. below). Such applications serve several of harmful bacteria found in manure.
Approximately half of all U.S. E. purposes: they provide an alternative Composting manure is common,
coli 0157:H7 outbreaks from produce or supplement to synthetic fertilizers, and is an effective way to reduce the
between 1982 and 2002 were due to they build levels of soil organic mat- presence of pathogens (Jiang et al.
contamination during food prepara- ter, and they provide a way to dispose 2003). However, the effectiveness of
tion; the other half were caused by of the large quantities of manure that composting practices in eliminating E.
contamination that occurred either accumulate in stockyards, feedlots, and coli 0157:H7 can depend on tempera-
in the field or during handling and dairy operations. However, manure ture, moisture, and composting time
processing (Rangel et al. 2005). Be- can incubate pathogens and contami- (Hess et al. 2004). Improper compost-
cause E. coli 0157:H7 is carried and nate crops in the field (Natvig et al. ing can result in crop contamination.
transmitted by animals, pre-harvest 2002). Pathogens have been shown The National Organics Program
contamination is typically linked to to be transferred from manure to the has specific composting requirements
animal feces from the applications surface of crops on contaminated for manure and other material used
of manure; cattle and domesticated soil particles. Once on the surface of in compost; these include the need for
animal operations; contaminated ir- the crop, pathogens may persist for defined carbon to nitrogen ratios, spe-
rigation water; contaminated flood extended periods of time (Islam et al. cific temperatures that must be reached
water; and direct contact with do- 2005, Beuchat 1999). during the composting process, and
mesticated or wild animals carrying Several studies suggest that the set lengths of composting time (NOP
pathogenic bacteria. composition of cattle diets can affect 2006). On the Central Coast, many
the bacteria found in manure. Diez- conventional growers follow Good Ag-
POSSIBLE SOURCES OF CROP Gonzalez et al. (1998) show that cattle ricultural Practices as outlined by their
CONTAMINATION IN THE FIELD fed grain have significantly higher buyers, which involve composting or
Contamination from Soil levels of E. coli than cattle fed hay aging manure before application (Rich-
Crops can be exposed to E. coli or cattle that were grazed on pasture. ard Smith, UCCE Monterey County
through contact with contaminated Another group of scientists explored Farm Advisor, pers. comm.)
soil (Francis et al. 1999). Fecal mate- the effects of different cattle diets on Due to possible risks from manure
rial from animals, especially livestock, E. coli 0157:H7 and Salmonella in to “ready-to-eat” crops such as lettuce
is a major source of soil contamina- manure from dairy cattle (Franz et al. and spinach, the application of raw
tion, with cattle identified as the most 2005). They found that manure from manure has been phased out on the
important reservoir of E. coli 0157: cattle with a pure hay diet had reduced Central Coast. Application of aged or
H7 (Nielsen et al. 2004). The 2006 levels of E. coli 0157:H7 and Salmo- composted manures (if used) is usually
contamination of spinach in the Sali- nella compared to manure from cattle limited to fall, to allow a substantial
nas Valley has been tentatively linked fed a combination of grass and maize window of time prior to spring plant-
to E. coli O157:H7 in cattle manure silage. They conclude that a high starch ing (R. Smith, pers. comm.).
that may have been spread by wild diet favors the growth and survival of Diverse microbial organisms in soil
pigs from cattle located less than a pathogenic bacteria. Because feeding may protect crops from contamination.
CENTER RESEARCH BRIEF #10 | Fall 2006 5
Food Safety and Environmental Protection
One study indicates that naturally oc-
Cattle have been identified
curring bacteria in soil can reduce the as a major source of E. coli
abundance of E. coli 0157:H7 and 0157:H7, which can spread
from contaminated manure.
inhibit the pathogen from uptake into
lettuce tissue (Johannessen et al. 2005).
Soil with diverse microorganisms may
contain Pseudomonas fluorescens, a
bacterium known to compete with and
inhibit the growth of E. coli. 0157:H7.
This study indicates that microbial
pathogens may flourish in soils that
lack a balance of natural microbial
diversity, and that soil management
should aim to encourage the diversity
of microbial organisms.
Organic fields have been shown to
host higher diversity and biomass of
soil microbial and faunal communities
that have been correlated with higher
suppression of soil-borne plant patho-
gens (Van Bruggen 1995). This pattern
may also hold for the suppression of taminated irrigation water increases Contamination from Direct Contact
pathogens such as E. coli 0157:H7. chances of contamination (Solomon with Animals
et al. 2003). Because E. coli 0157:H7 originates
Contamination from Water Sources
Contamination likely occurs from animals, crop contamination can
Water can also transport pathogens
through direct contact between the occur through direct contact with ani-
to crops. Rivers, creeks, or streams that
above-ground portions of crops and mals. Domestic cattle are the primary
are diverted and used for irrigation
contaminated water; however, studies source of microbial pathogens associ-
may contain pathogenic bacteria from
show that if concentrations are high ated with food-borne illness.
upstream activities, such as livestock
enough, it may be possible for E. coli Prevalence can vary among cattle
operations. Runoff from open lot
0157:H7 to enter crops through the depending on the location and the sea-
cattle grazing areas and concentrated
roots. son. A study in the Pacific Northwest
animal operations has been shown to
One study inoculated irrigation wa- revealed that 3.6% of feedlot cattle
contain harmful pathogens (Vinton et
ter with extremely high concentrations and 2.3% of dairy cattle tested positive
al. 2004). Water draining from both
of E. coli 0157:H7 and found that for E. coli. 0157:H7 (Hancock et al.
open lot grazing operations and con-
the pathogen entered the plant tissue 1998). Another study in England tested
centrated animal operations should
without surface exposure (Solomon et cattle over an entire year and found
be managed to prevent contaminated
al. 2002). However, the authors of this that 13.4 % of beef cattle and 16.1%
runoff (Koelsch et al. 2006).
study admit that the concentrations of of dairy cattle tested positive for E.
Due to the possibility of water con-
E. coli 0157:H7 used far exceed any coli. 0157:H7. However, in spring and
tamination from livestock or human
that would be found on an agricultural summer, up to 36.8% of total cattle
waste, it is recommended that food
field. Another group of scientists found tested positive for E. coli. 0157:H7
crops not be irrigated with water from
that the ability for contamination to (Chapman et al. 1997). Another study
unknown sources and with unknown
occur through the root system appears in North Dakota also illustrates that
microbial content (Solomon et al.
to be dose dependent, although the prevalence in cattle changes depend-
2002). Flooding of nearby contami-
specific level at which this occurs is ing on the season and found that up
nated water bodies onto fields can also unknown (Wachtel et al. 2002a). to 53% of cattle tested positive for E.
result in contamination of crops. In a more realistic scenario, scientists coli. 0157:H7 in the spring (Khaitsa
Studies have also investigated how investigated cabbage that was irrigated et al. 2006).
different methods of irrigation can af- with creek water contaminated by a There are also concerns that wild
fect the risks of crop contamination. sewage spill (Wachtel et al. 2002b). animals can be sources or vectors
One study found that lettuce is more Here, they found that although the of food-borne pathogens. Research
likely to test positive for E. coli. 0157: roots were contaminated by E. coli, the has shown that wild animals exhibit
H7 if exposed through contaminated edible portions of the plant were not. relatively low levels or an absence of
sprinkler water than through contami- In the absence of exceedingly high con- of E. coli O157:H7. A study in the
nated surface water (Solomon et al. centrations of pathogens, direct surface Pacific Northwest did not find any E.
2002). Another study also found that exposure to contaminated water is the coli. 0157:H7 from 300 samples of
spraying crops repeatedly with con- likely route of contamination. rodents on cattle farms (Hancock et al.
6 CENTER RESEARCH BRIEF #10 | Fall 2006
Center for Agroecology & Sustainable Food Systems
1998). Rodents can be divided into two Although most studies have looked lettuce and leafy green vegetables
groups: field rodents and commensal at gulls, which are often associated created by cooperative efforts in the
rodents, such as house mice and rats with human waste, fewer studies have industry. In April of 2006, “Commod-
(Meerburg et al. 2004). Commensal looked at other types of wild birds. A ity Specific Food Safety Guidelines for
rodents may be in closer contact with study of Canada Geese in New Jersey the Lettuce and Leafy Greens Supply
humans and waste, whereas field and Virginia showed no signs of E. Chain”(Gombas et al. 2006) was re-
rodents that are kept separated from coli 0157:H7 (Converse et al. 1999). leased by a group of associations in the
these sources of contamination may A study of passerines and woodpeckers lettuce and leafy greens industry.
have a much lower prevalence of carry- in Wisconsin showed that of 364 birds, Although the specific causes of
ing pathogens. Field rodents should be no birds showed signs of Salmonella recent E. coli O157:H7 outbreaks
managed to minimize their exposure to and 1% showed signs of E. coli 0157: on the Central Coast have not been
livestock (Meerburg et al. 2004). H7 (Brittingham, et al. 1988). Another pinpointed, industry-led guidelines
Several studies have explored the study in the Pacific Northwest looked now call for “clean” fields and many
role of wild deer as vectors. In a study at wild birds on cattle ranches and buyers insist on food safety audits to
of white-tailed deer sharing a range- found that no birds showed signs of ensure that such guidelines are being
land with cattle in Kansas, 2.4% of E. coli 0157:H7 (Hancock et al. 1998). followed. These guidelines and audits
deer carried E. coli 0157:H7 (Sargeant These studies indicate that the presence encourage growers to reduce the pres-
et al. 1999). Another study in the of pathogens may be higher in birds ence of wildlife and any non-crop
southeastern United States found that associated with human waste, such as vegetation such as shrubs and grasses
0–0.6% of wild white-tailed deer shar- gulls, than in wild birds such as wood- that could attract wildlife, as seen in
ing a range with cattle showed signs of peckers, chickadees, and nuthatches, the following excerpts:
E. coli 0157:H7. The study concluded which are associated with more natural “high concentrations of wild-
that wild deer are not a major reser- environments. life (such as deer or waterfowl
voir of E. coli 0157:H7 (Fischer et al. in a field) may increase the
2001). FOOD SAFETY GUIDELINES CONFLICT potential for microbial contami-
Many studies have investigated WITH ENVIRONMENTAL GOALS nation. Control of wild animal
the possibility of birds as a source of Although there are currently no populations in the field may be
food-borne illness. Studies in England mandatory pre-harvest regulations difficult, especially where crop
surveyed gulls and showed that the to prevent contamination of crops in production areas are adjacent
prevalence of E. coli 0157:H7 in feces the field, increased awareness of food to wooded areas, open mead-
can range from 2% (Wallace et al. safety issues has placed considerable ows, and waterways. . . . where
1997) to 12.9% (Fenlon 1981). An- pressure on growers to meet high high concentrations of wildlife
other study in Sweden found that 4% safety standards. Since it is unknown are a concern, growers should
of gulls sampled contained Salmonella at which stage microbial contaminants consider establishing good ag-
isolates, and of 151 wild passerines are introduced, guidelines have been ricultural practices to deter or
(landbirds) and gulls none contained developed for farming practices to redirect wildlife to areas with
E. coli (Palmgren et al. 1997). augment rules in place for packing, crops that are not destined for
handling, and processing. The U.S. the fresh produce market.”2
Department of Health and Human Ser-
“Evaluate the need for bare
vices through the U.S. Food and Drug
soil buffers to adjacent land that
Administration (FDA) has produced
may encourage high populations
several publications, including the
of reptiles, amphibians, rodents,
“Guide to Minimize Microbial Food
birds or other potential sources
Safety Hazards for Fresh Fruits and
of contamination.”3
Vegetables” (1998) and the “Analysis
and Evaluation of Preventive Control “Monitor and minimize do-
Measures for the Control and Reduc- mestic and wildlife activity in
tion/Elimination of Microbial Hazards lettuce/leafy greens fields and
on Fresh and Fresh-Cut Produce” production environments (e.g.
(2001). In addition, a national Good reduce potential cover and har-
Agricultural Practices (GAP) program
has created voluntary guidelines and 2U.S. Department of Health and Human
educational material to encourage safe Services, Food and Drug Administra-
farming practices. tion, Center for Food Safety and Applied
Farming organizations and private Nutrition Guide to Minimize Microbial
food safety auditors have developed Food Safety Hazards for Fresh Fruits and
their own guidelines. These include Vegetables (October, 1998)
Studies of deer have shown that they carry
relatively low or no traces of E. coli 0157:H7, commodity-specific guidelines for 3National GAP (Good Agricultural Prac-
even when sharing range with cattle. cantaloupe and more recently for tices) Program
CENTER RESEARCH BRIEF #10 | Fall 2006 7
Food Safety and Environmental Protection
borage, eliminate standing water, D
Vegetated buffers ia
utilize animal repellants and at- of native perennial na
tractants).”4 plants can filter pol- Stu
lutants and sediment a
Although wildlife are presented as a while providing rt
serious risk in these guidelines, the sci- habitat for beneficial
insects.
entific studies discussed earlier do not
confirm that wildlife are a significant
threat. But because wildlife has been
identified as a source of contamina-
tion, growers are facing pressure to
remove potential habitat. This pres-
sure to create “clean” fields places
growers in a Catch-22 situation, as
market-based demands to follow food
safety guidelines may substantially de-
ter the adoption of practices to address
regional environmental problems,
thus increasing pollution and habitat COULD ENVIRONMENTAL PRACTICES BE approximately 40 field trials indicat-
degradation. USED TO REDUCE CONTAMINATION? ing that vegetative systems with a
Past and current pre-harvest Despite contradictions in current settling basin can significantly reduce
guidelines have been voluntary and pri- food safety and environmental guide- pollutants, including pathogenic bac-
marily market-driven, but with public lines, certain environmental practices teria. Other studies indicate that fecal
concern over food safety increasing, the may actually be useful in addressing coliform reductions greater than 90%
U.S. Food and Drug Administration has food safety problems. Although the are regularly observed from vegetated
expressed a need to create mandatory goal of many practices is to reduce treatment systems (Kadlec and Knight
farming standards. Recently, owners erosion and pollution from fertil- 1996). Vegetated systems may reduce
of the nation’s largest supermarket izers and pesticides, these practices the presence of pathogenic bacteria in
chains, including Safeway, Albert- can also remove and control harmful waterways near fields and significantly
sons and Ralph’s grocery chains, and microbes. Vegetated buffers, grassed reduce the possibility of contamination
Costco Wholesale Corporation, have waterways, and constructed wetlands if flooding occurs.
demanded that growers work with fed- can be effective ways to reduce levels Constructed wetlands can effective-
eral regulators, academia and industry of waterborne pathogens, including ly reduce the presence of pathogenic
research scientists to standardize food- E. coli. bacteria and are already used in sewage
safety requirements, including the Vegetated buffers can reduce the and agricultural wastewater treatment.
compatible use of adjacent farmland. transfer of pathogenic bacteria in In a wetland, pathogens are removed
The grocers’ consortium threatens to surface water. Contamination in through filtration in dense vegetation,
set up their own certification system if overland flow may be reduced by sedimentation of particles carrying
such standards are not quickly estab- using filtration through perennial for- pathogens, microbial competition and
lished and enforced (Hirsch 2006). age and/or grasses. Tate et al. (2006) predation, high temperatures, and UV
As industry and government tested the effectiveness of E. coli disinfection (Hench et al. 2003, Nokes
personnel weigh the option of con- filtration through vegetated buffers et al. 2003, Greenway et al. 2005).
verting current industry guidelines on cattle grazing lands in California. Nokes et al. (2003) show that large,
into mandated regulations and adding They used known quantities of E. coli as well as small-scale, constructed
additional rules for farming practices, and measured transport in surface wetlands can reduce levels of fecal
it is critical that these guidelines be water runoff. Although the efficiency coliforms by up to 97%.
evaluated to understand the full of filtration depends on water flow, Hench et al. (2003) tested the ef-
implications of their widespread adop- soil type, and slope, they found that fectiveness of constructed wetlands at
tion, both for protecting consumer vegetative buffers are an effective way removing specific pathogenic bacteria.
health as well as for their impact on to reduce inputs of waterborne E. coli They show that within a 23–52 hour
environmental quality. If current “vol- into surface waters. Buffers already wetland residence time Salmonella
untary” guidelines become mandatory, used for environmental practices could levels can be reduced by 93–96%. Hill
environmental efforts in the Central be more specifically designed to reduce and Sobsey (2001) also report a 96%
Coast region and elsewhere could be E. coli transport. reduction in Salmonella in wastewater
substantially undermined. Grassed waterways and vegetated from a pig farm after passing through
treatment systems within bodies of a constructed wetland. Another study
4Commodity Specific Food Safety Guide- water have also been shown to reduce also shows that constructed wetlands
lines for the Lettuce and Leafy Greens the presence of pathogens. Koelsch et can remove 95% of pathogens and
Supply Chain (March 2006) al. (2006) reviewed studies and found indicator organisms (Greenway 2005).
8 CENTER RESEARCH BRIEF #10 | Fall 2006
Center for Agroecology & Sustainable Food Systems
S Vegetation buffers a Some fear that the use of environ-
C
NR Monterey County wet- mental practices may increase the
DA laann add fjraocmen itm apraticcthso okfe presence of wildlife near cropped fields
S
U operation. and that wildlife represent a signifi-
s,
ett cant threat to food safety. However,
n B studies in other regions of the US
n
y illustrate that wildlife, such as birds
L
by and small mammals, are usually not
o
ot hosts of pathogens associated with
h
P food-borne illness. To resolve these
issues confidently, additional research
may be needed to investigate the role
of wildlife as vectors of pathogens in
the Central Coast.
Some of this research is already in
the works: in a current USDA-funded
study, crews will collect thousands
Through their literature review, Gre- outbreaks of food-borne pathogens. It of samples of domestic animal and
enway et al. (2005) conclude that is likely that the environmental prac- wildlife droppings; creek, ditch and
surface-flow constructed wetlands tices discussed in this brief that use irrigation water; and farm soil and let-
with a high diversity of macrophytes non-crop vegetation will attract some tuce growing on Salinas Valley farms
can reclaim water and produce efflu- wildlife. However, the relative risks in an attempt to identify sources of
ent meeting microbial standards for need to be weighed. Studies indicate E. coli O157:H7. Data collected in
agricultural irrigation. Lastly, Nokes et that on average about 1% of wildlife the field will be carefully analyzed
al. (2003) show that heavily vegetated associated with natural environments to identify the vertebrates that are
wetlands remove more harmful bacte- carry bacteria that are pathogenic for sources of E. coli O157:H7, assess
ria when compared to non-vegetated humans. If this statistic is also true for the climate, landscape attributes and
wetlands. wildlife in the Central Coast, the ben- irrigation management practices that
These practices, which are also used efits of using environmental practice to are correlated with increased risk of
to enhance environmental quality, may reduce contamination may outweigh contamination, and determine whether
be designed specifically to increase possible threats from wildlife. contaminated lettuce is associated
the effectiveness of reducing harmful with certain farming practices or en-
pathogens in agricultural settings. For CONCLUSION vironmental factors (University of
example, constructed wetlands can With increasing pressure to address California Agriculture and Natural
be designed to maximize the removal problems with food safety and the Resources 2006).
of pathogens (Greenway et al. 2005). possibility of mandatory standards for Despite the need for additional
With further research, design standards farming practices, it is a critical time to research, the studies presented in this
tailored to pathogen removal could be evaluate the potential impact current brief suggest that the goals of environ-
created for each of these environmental food safety guidelines could have on mental protection and safe food can
practices. efforts to improve the environmental both be achieved on the Central Coast.
Ways to make the adoption of these sustainability of farming operations. Current food safety guidelines may be
practices more feasible can also be Converting guidelines calling for the exaggerating the role of wildlife and
explored. For example, Nokes et al. removal of non-crop vegetation into unnecessarily pressuring growers to re-
(2003) show that small-scale vegetated regulations could represent a major move non-crop vegetation intended to
wetlands can be equally effective and setback in efforts to address water pol- improve water quality. The widespread
efficient at removing harmful bacteria lution on the Central Coast. However, removal of this vegetation would sub-
as large-scale constructed wetlands. scientific studies, such as those present- stantially set back water quality efforts
Given the high values of both land ed in this paper, show that the goals of and increase pollution in agricultural
and crops in the region and the costs safe food and a healthy environment watersheds. In addition, studies indi-
associated with construction, these may not be mutually exclusive. Certain cate that these non-crop vegetation
small-scale wetlands as well as smaller environmental practices already used measures could also be removing and
vegetative buffers and treatment sys- to reduce pollutants associated with reducing the presence of pathogenic
tems may be easier to apply on the agriculture may also be used to con- bacteria, such as E. coli O157:H7,
Central Coast. tain and absorb harmful pathogens. in agroecosystems. Their widespread
When assessing the overall impact More research is needed to identify removal could actually increase risks
of environmental practices on the the effectiveness of these practices in of crop contamination.
safety of food, different risks must be addressing food safety issues specific Before further steps are taken to-
considered. Wildlife is often blamed for to the Central Coast. ward mandatory farming standards
CENTER RESEARCH BRIEF #10 | Fall 2006 9
Food Safety and Environmental Protection
that emphasize “clean” fields, it is birds. Journal Of Wildlife Diseases numbers of Salmonellae in gull feces.
critical that industry leaders, conserva- 24(2): 299-307. Journal of Hygiene 86(2): 195-202.
tion organizations, and government Bureau of the Census, US Department of Fiener, P., and K. Auerswald. 2003.
agencies work together, using all avail- Commerce. Per capita utilization of Concept and effects of a multi-pur-
able information, to resolve current selected commercially produced fresh pose grassed waterway. Soil Use and
conflicts and create workable solutions fruits and vegetables: 1970-1994. Sta- Management 19(1): 65-72.
to both the food safety and environ- tistical Abstract of the Unites States, Fiener, P., and K. Auerswald. 2003. Ef-
mental issues that currently challenge 116th Edition. Washington DC: US fectiveness of grassed waterways in
Central Coast agriculture. Government Printing Office. reducing runoff and sediment delivery
Caffrey, J. 2001. Biogeochemical cycling, from agricultural watersheds. Journal
in Changes in a California estuary: a of Environmental Quality 32(3):
References
profile of Elkhorn Slough. Caffrey, 927-936.
Altekruse, S. F., M. L. Cohen, and D. J., M. Brown, and W. B. Tyler (eds). Fischer, J. R., T. Zhao, M. P. Doyle,
L. Swerdlow. 1997. Emerging food- Moss Landing, CA: Elkhorn Slough M. R. Goldberg, C. A. Brown, C. T.
borne diseases. Emerging Infectious Foundation. Sewell, D. M. Kavanaugh, and C. D.
Diseases 3(3): 285-293. Chapman, P. A., C. A. Siddons, A. T. Bauman. 2001. Experimental and
Beuchat, L. R. 1996. Pathogenic mi- Cerdon Mal.o, and M. A. Harkin. field studies of Escherichia coli O157:
croorganisms associated with fresh 1997. A 1-year study of Escherichia H7 in white-tailed deer. Applied and
produce. Journal of Food Protection coli O157 in cattle, sheep, pigs and Environmental Microbiology 67(3):
59(2): 204-216. poultry. Epidemiology and Infection 1218-1224.
Beuchat, L. R. 1999. Survival of entero- 119(2): 245-250. Francis, G. A., C. Thomas, and D.
hemorrhagic Escherichia coli O157: Converse, K., M. Wolcott, D. Docherty, O’Beirne. 1999. The microbiological
H7 in bovine feces applied to lettuce and R. Cole. 1999. Screening for safety of minimally processed veg-
and the effectiveness of chlorinated potential human pathogens in fecal etables. International Journal of Food
water as a disinfectant. Journal of material deposited by resident Canada Science and Technology 34(1): 1-22.
Food Protection 62 (8): 845-849. geese on areas of public utility. USGS Franz, E., A. D. van Diepeningen, O.
Beuchat, L. R. 2002. Ecological factors National Wildlife Health Center. FWS J. de Vos, and A. H. C. van Brug-
influencing survival and growth of ALC 14-16-0006. gen. 2005. Effects of cattle feeding
human pathogens on raw fruits and Dabney, S. M., M. T. Moore, and M. A. regimen and soil management type
vegetables. Microbes and Infection Locke. 2006. Integrated management on the fate of Escherichia coli O157:
4: 413-423. of in-field, edge-of-field, and after- H7 and Salmonella enterica serovar
Beuchat, L. R. 2006. Vectors and condi- field buffers. Journal of the American Typhimurium in manure, manure-
tions of preharvest contamination of Water Resources Association 42(1): amended soil, and lettuce. Applied
fruits and vegetables with pathogens 15-24. and Environmental Microbiology
capable of causing enteric diseases. Davidson, C. 2004. Declining down- 71(10): 6165-6174.
British Food Journal 108(1): 38-53. wind: Amphibian population declines Gorny, J.R., H. Giclas, D. Gombas, and
Beuchat, L. R. and J. H. Ryu. 1997. in California and historical pesticide K. Means. 2006. Commodity specific
Produce handling and processing use. Ecological Applications 14(6): food safety guidelines for the lettuce
practices. Emerging Infectious Dis- 1892-1902. and leafy greens supply chain. April
25, 2006. http://www.cfsan.fda.
eases 3(4): 459-465. Davidson, C., H. B. Shaffer, and M.
gov/~acrobat/lettsup.pdf (Viewed:
Blanco-Canqui, H., C. J. Gantzer, S. H. R. Jennings. 2001. Declines of the
October 11, 2006).
Anderson, E. E. Alberts, and A. L. California red-legged frog: climate,
Thompson. 2004. Grass barrier and UV-B, habitat, and pesticides hypoth- Greenway, M. 2005. The role of con-
vegetative filter strip effectiveness in eses. Ecological Applications 11(2): structed wetlands in secondary
reducing runoff, sediment, nitrogen, 464-479. effluent treatment and water reuse in
subtropical and Australia. Ecological
and phosphorus loss. Soil Science Di, H. J., and K. C. Cameron. 2002.
Engineering 25(5): 501-509.
Society of America Journal 68(5): Nitrate leaching in temperate agro-
1670-1678. ecosystems: sources, factors and Hancock, D. D., T. E. Besser, D. H. Rice,
E. D. Ebel, D. E. Herriott, and L. V.
Bridges, A. 2006. Wild pigs eyed in mitigating strategies. Nutrient Cycling
Carpenter. 1998. Multiple sources
tainted spinach probe. San Francisco in Agroecosystems 64(3): 237-256.
of Escherichia coli O157 in feedlots
Chronicle, October 26, 2006. Diez-Gonzalez, F., T. R. Callaway, M. and dairy farms in the northwestern
Briggs, J. A., T. Whitwell, and M. B. Ri- G. Kizoulis, and J. B. Russell. 1998. USA. Preventive Veterinary Medicine
ley. 1999. Remediation of herbicides Grain feeding and the dissemina- 35(1): 11-19.
in runoff water from container plant tion of acid-resistant Escherichia Haycock, N. E. and G. Pinay. 1993.
nurseries utilizing grassed waterways. coli from cattle. Science 281(5383): Groundwater nitrate dynamics in
Weed Technology 13(1): 157-164. 1666-1668. grass and poplar vegetated riparian
Brittingham, M. C., S. A. Temple, and Fenlon, D. R. 1981. Seagulls (Larus spp.) buffer strips during the winter. Jour-
R. M. Duncan. 1988. A survey of the as vectors of Salmonellae—an investi- nal of Environmental Quality 22(2):
prevalence of selected bacteria in wild gation into the range of serotypes and 273-278.
10 CENTER RESEARCH BRIEF #10 | Fall 2006