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This document discusses the health hazards of consuming fruits and vegetables that may contain contaminants produced if they are grown over septic drainfields or too close to other sources of effluent from septic systems or on-site waste disposal systems
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Can Sewage Pathogens & Contaminants Appear at Unsafe Levels in Fruits and Vegetables Grown Near Septic Drainfields?
We include discussion of health or other concerns with soil and groundwater contamination and with measures adopted to address these problems. Our page top photo shows the author (DJF) inspecting a vegetable farm near Frankfort, Germany in 1968.
Readers should also see our safe-planting discussion at Gardens Near Septics and see our discussion of pathogens in sewage at SEWAGE PATHOGENS in SEPTIC SLUDGE: what makes up the contents of residential sewage? and also SEWAGE NITROGEN CONTAMINANTS - a second important type of septic effluent contamination. Anyone working on or around or owning a septic tank should be sure to see SEPTIC & CESSPOOL SAFETY. We discuss the risk of tree or plant damage to septic drainfields at SEPTIC SYSTEMS, PLANTS OVER.
The short answer is yes, at least some contaminants and pathogens found in sewage and sewage effluent may be present in fruits and vegetables grown on or close to septic system components that deliberately (drainfields, cesspools, drywells) or accidentally (leaky septic tanks or broken septic or sewer piping) place septic or sewage effluent in soils near plants.
Studies such as the one described below did not find that all pathogens appear in fruits and vegetables grown over or near a septic drainfield. For example Staphylococcus aureum was not detected in the study below. But twenty-two other dangerous pathogens - enterobacteriaceae were indeed found. The
vegetables tested in the study we discuss below were tomato, radish, cucumber,
eggplant, potato, pepper, garden pea, gourd,
zucchini, artichoke, broad bean, turnip, onion,
In "Bacterial Pathogens Recovered from Vegetables Irrigated by Wastewater in Morocco", a study of the occurrence of pathogenic bacteria in vegetables irrigated by untreated wastewater, published in June 2007, Y. Karamoko et als, (quoting from the article abstract) The authors obtained 50 vegetable samples from various regions in Morocco and examined them to determine the micro biological quality of these products. Aerobic count, coliform, enterococci, and Staphylococcus areus were evaluated. ... The results clearly demonstrated that vegetables irrigated with untreated wastewater have a high level of microbiological contamination. ... The large number of total microorganisms
Also quoting from the above study,
The vector of contamination of fruits and vegetables from septic effluent includes multiple paths. The authors point out that ... vegetables can become contaminated with pathogenic organisms during growth, harvest, post harvest handling, or distribution (McMahon Sr Wilson, 2001). Use of untreated wastewater in irrigation represents an important route for transmission of these pathogenic organisms.
So does a private septic tank and drainfield adequately treat septic effluent so that it is not a risk to crops or fruits grown nearby? Effluent discharged from a septic tank is not "untreated" - rather it is "partly treated". It is not "fully treated". We interpret this to mean that while the risk of contamination of fruits and vegetables grown over or close to a septic drainfield may be less than that found in this study, it is certainly not zero.
The level of wastewater treatment by conventional septic tanks is typically less than 20% to no more than 45%. (Jantrania). Advanced wastewater treatment systems, if the system is properly installed, designed, maintained, and is working, can treat effluent more effectively to 70%.
Jantrania points out that small wastewater treatment systems can produce good results, capable of producing exceptional quality as good as large municipal wastewater treatment systems. While Jantrania (p. 5) asserts that "Complete recycling of wastewater to drinking water standards with onsite treatment is feasible", we pose that such a level of treatment at private onsite treatment systems (residential septic tanks, drainfields, even AEROBIC SEPTIC SYSTEMS, or MEDIA FILTER SEPTIC SYSTEMS, and other SEPTIC SYSTEM DESIGN ALTERNATIVES) in practical application rarely, perhaps never, reaches that standard except where special sterilizing equipment and systems are installed.
Bacterial Pathogens from Septic Effluent Can Survive in Soil and Transfer through Vegetables to Humans
The authors Y. Karamoko et als, continued:
Our conclusion is that unless you have obtained specific and reliable tests indicating otherwise, consuming fruits or vegetables grown in soil fed by septic effluent pose a health risk.
Our OPINION is that the health risk from such foods ma be even more serious for people at extra risk due to fragile health, such as people whose immune systems are weakened or compromised, undergoing chemotherapy, for example, the elderly, infant, or people suffering from immune-related disorders. Discuss these risks with your doctor.
at BACTERIAL PATHOGENS in FRUIT & VEGETABLES is a slightly-rough online copy of the original article.
Factors Affecting Risk of Pathogenic Contamination of Vegetables or Fruits Grown over a Septic Drainfield
At Gardens Near Septics we stated that planting a fruit or vegetable garden over or near septic system components raises some important questions:
It seems likely that the following variables will affect the level of contaminants picked up by vegetables or fruits grown on or over private septic drainfields and effluent disposal systems:
OPINION: At Using Root Killers we discuss using chemicals to try to "clear" septic system piping and drainfields. These products include a range of chemicals whose product-description ranges from "safe and harmless" to "toxic -keep out of reach of children".
We have not yet found studies of toxic chemicals picked up by fruits and vegetables grown near septic systems from chemical treatment sources. Contact Us if you have information.
OPINION: A second category of possible "chemical " contaminants from sewage includes heavy metals that may be present in sewage or septic effluent. See SEPTIC TREATMENTS & CHEMICALS for more information and warnings.
Frequently Asked Questions (FAQs) About Sewage Contamination of Fruits & Vegetables - & Need for Further Research
The Y. Karamoko et als, article discussed here is one of the most important contemporary research projects performed to study the risk of contaminants entering human food through wastewater. But interpreting the actual level of risk to a homeowner whose garden is close to or even atop a septic drainfield, and where raw sewage wastewater is not being used to directly irrigate fruits or vegetables, some important questions remain.
The questions that we pose below are intended to assist in translating the level of contamination found in the Y. Karamoko et als, study, "Bacterial Pathogens Recovered from Vegetables Irrigated by Wastewater in Morocco", Y. Karamoko, K. Ibenyassine, M. M. Ennaji, B. Anajjar, R. Ait Mhand, M. Chouibani, Journal of Environmental Health, June 2007, (wastewater irrigated plants) and the level of pathogens that might be expected to be found in fruits and vegetables grown over a common residential septic drainfield?
Question 1: How completely did the authors separate possible fruit/vegetable contaminant sources- plant root system vs. plant surfaces: contaminants arising through the soil and through a plant's root system need to be described separately from contaminants that may be lodged on the surface of a fruit or vegetable from dust, wet soil splash-up during rain, during handling?
The study cites indicates "The vegetable samples were collected in sterile polyethylene bags, and steps were taken to avoid contamination of the vegetables by soil or other contamination sources." and " Each sample was rinsed several times with sterile distilled water to eliminate the soil."
What might be unanswered is the effect of the duration of time that dust, or unsanitary water splash-up rested on plant surfaces before the plants were washed in the lab, and the extent to which pathogens may have been absorbed into the plant system through its surfaces rather than its root system.
Question 2: How do planting, soil specifics, plant root depths, septic drainfield design, high seasonal water table and type of plant affect the uptake of sewage contaminants into fruits or vegetables grown over a conventional septic drainfield compared with the uptake of sewage contaminants into these same plants when direct irrigation is performed using sewage or septic effluent?
The authors were aware of this question, as the study cites "The actual risk of disease transmission, however, is related to whether this survival time is long enough to allow transmission to a susceptible host. The crop and the field are the link between the pathogen in the wastewater and the potential for infection. The factors controlling transmission of disease are agronomic examples of such factors are the crop grown, the irrigation method used to apply wastewater, and cultural and harvesting practices. "
And "Guo and co-authors have demonstrated that soil and water are potential reservoirs from which Salmonella can contaminate tomatoes (Guo, Chen, Brackett, & Beuchat, 2002). ... That study provided evidence that Salmonellae can be transported from an inoculated nutrient solution to the hypocotyls, cotyledons, stems, and leaves of young tomato plants."
We understand the study to assert that dust and splash-up onto plant surfaces ("aerial tissues") could be a source of the pathogens found in the study, as well as roots "tissues in contact with inoculated soil".
This combination of pathogen sources may make it more difficult to translate the results of this study to a level of risk for plants grown over septic drainfields, systems where effluent is not being applied directly to the surface of soils but rather is being distributed underground.
Question 3: What assays were made of the level of contaminants in the irrigating sewage or septic effluent that was used to irrigate the studied fruits and vegetables?
We did not find this information included in the study except for a general description of the types of contaminants found in wastewater used for irrigation in many countries.
Question 4: What differences should we expect to find between the level of contaminants in the irrigating sewage or septic effluent used in the areas studied compared with the level of contaminants in private onsite septic system effluent flowing into a septic drainfield?
OPINION: This is the chief question that needs to be answered in extending the results of this important study to the question of the level of pathogens that may be found in garden vegetables or fruits planted over or close to a conventional septic system drainfield in which effluent is disposed-of entirely below ground.
OPINION: A second level of risk is likely to be found in alternative septic system designs (aerobic or ATU systems used for example in the Southwestern U.S.). Although aerobic ATUs achieve a higher level of treatment, in some private septic system designs the effluent from those systems is dispersed to the ground surface using sprays. The benefit of higher level of treatment of wastewater may be offset by its surface application if property owners grow edible foods nearby.
Question: If my avocado and mango trees are planted near, within three meters of my septic tank, are they safe to eat? -- Cheryl Sweetland
Answer: OPINION: Well, the answer is a definite "maybe". Or as ASHI Educator Mark Cramer says, "It depends."
In theory, a septic tank that is working correctly never overflows or floods. Sewage and septic effluent stay safely inside the tank and effluent flows out of the septic tank through solid piping (not perforated piping) to a drainfield or to a distribution box that then connects to the drainfield.
If your trees are a safe distance from the drainfield and if the septic tank is not leaky, and if no one spills sewage all around the tank during pumping, your mangos and avocados are probably fine to eat. at SEPTIC SYSTEMS, PLANTS OVER we discuss issues of planting anything over or near septic system components. If your trees are close to the septic tank there are two other risks:
If your septic tank is home-made or "site built" or if it is a cesspool, it is much more likely that tree roots will invade and damage the system and that fruit on those trees may be contaminated as well.
If you don't know where the drainfield is actually located on your property, it would be smart to find it. See SEPTIC DRAINFIELD LOCATION.
What Pathogens are found in Sewage?
See SEWAGE PATHOGENS in SEPTIC SLUDGE for a list and discussion of of the common pathogens and other contaminants in residential sewage
Reader Comment: A garden over a drainfield does not present the same risks as using sewage directly on crops - tree crops may be ok
I recently found your site and find it very useful. Being very interested and reasonably well educated in wastewater and reuse I found your review of the septic system and gardens interesting (I like fining new articles) but perhaps too conservative and too have missed an important point.
The Morocco paper refers to harvest of vegetables with untreated wastewater as you mention but most importantly the wastewater is applied at the soil surface. This is very different from growing a garden on top of a drainfield. In a well operating drainfield (i.e. no surfacing sewage) the septic tank effluent is well treated and will only be in contact with the plant roots.
A review of the literature shows that this mechanism of transport for pathogens into healthy plants is unlikely, particularly in tree crops.
Best regards, Peter Burgoon, PhD, P.E. Water Quality Engineering, Inc.
Reply: Ok to grow food crops over a septic drainfield? It depends ...
Mr. Burgoon your point about the lower risk of sewage pathogens in tree crops is well taken, though that too may need some clarification.
For example in the case of some fruit crops (mangos, papaya) grown in Mexico and Central and South America there has long been a concern for and history of septic pathogens in [or on] those foods.
Testing those fruits for coliform or other contaminants is tricky because often they are harvested, transported, stored, and sold under dusty conditions during which contaminants may settle onto the skin or surface of the fruit even though contemporary growing conditions themselves may not be a source of contamination.
Certainly out of the U.S. it is good practice (and a commonly followed procedure) to wash all fruits and vegetables in a suitable disinfectant (we use SinBac®) before consuming them. This disinfection step removes contaminated surface dust or bacteria that may have been placed thereon by handling. [We discuss SinBac at CHLORINE DISINFECTANT for Drinking Water ]
The topic of what can be grown over a septic drainfield continues to interest many of our readers. My OPINION, for which I'd appreciate argument from you, is ... it depends.
Risk of drainfield damage from gardening activities
Risk of pathogens entering food crops grown over or near septic drainfields or soakaway beds?
By no means do we want our content to be inappropriately scary or to give improper guidance about growing crops on or near drainfields; We've had difficulty finding expert authoritative papers and articles on the topic, so we welcome any further comment or citations you can offer.
Questions & answers or comments about gardens and fruit trees located close to septic system
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