Use of Reclaimed Water and Sludge in Food Crop Production (1996) / Chapter Skim
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6 Public Health Concerns About Chemical Constituents in Treated Wastewater and Sludge
6 Public Health Concerns About Chemical Constituents in Treated Wastewater and Sludge
Pages 100-119
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From page 100... ...
For the purpose of this review, non-metallic trace elements, such as selenium, are grouped together with the heavy metals under the more general designation of "trace elements." The following discussion first considers the fate of organic compounds from sludge and wastewater applications to soil. The uptake of these chemicals into plants and animals that go into the human food chain is then examined.
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From page 101... ...
Both laboratory and field experiments suggest that during land treatment, most pesticide residues are adsorbed by soil particles and remain sorbed on surface soils until degraded by microorganisms or volatized (Cork and Krueger, 19911. The relative degree of intrinsic biodegradability of toxic organics on the EPA Priority Pollutants list was illustrated by Tabak et al.
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From page 102... ...
the low concentration of the organics in reclaimed wastewater applied to crops may not support the level of microbial activity necessary for biodegradation in the soil environment. Literature on the microbial decomposition of toxic organics in soil is diverse (Alexander, 1994~.
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From page 103... ...
Phthalate Esters Phthalate esters, which are the most common toxic organic compounds in sludges, present little risk because plants serve as effective detoxifying barriers to these chemicals and prevent their accumulation in the food chain (Aranda et al.
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are produced by incomplete combustion. They are among the most common toxic organics in sludges (EPA, 1990~.
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From page 105... ...
The PCB concentrations in all tissues were less than 0.3 mg/kg; concentrations in carrot peels were greatest, followed in decreasing order by carrot tops; cabbage wrapper, inner leaves, and carrot core; corn ear leaf, stover, and corn grain. In general, the concentrations of PCBs in the plant tissues were indepenclent of the PCB concentration in soil.
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From page 106... ...
Their presence in treated sludge or reclaimed wastewater that is applied to agricultural land used for food crop production may be viewed by food processors as an additional uncontrollable pesticide burden, and they have expressed concern about their product quality being compromised when treated sludge and wastewater are used in food crop production (National Food Processors Association, 19921. Residues of aldrin and dieldrin were detected in 3 and 4 percent, respectively, of the 209 sludges surveyed in the NSSS, at concentrations of 0.002 mg/kg and at LOD, respectively (Kuchenr~ther and Carr, 1991~.
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From page 107... ...
Even if present at high initial concentrations, dioxin s in sludge would be cliluted at least 100-fold at agronomic sludge application rates, and the organic matter with the sludge would increase soil sorption capacity and likely reduce volatilization. Volatile Aromatic Compounds (VOC)
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From page 108... ...
Finally, because the fraction of sludge-borne toxic organics that does remain in soil has low bioavailability, absorption by crops is negligible. In some cases, volatile toxic organics may contaminate plant tissue through absorption of volatilized compounds; however, management practices, such as incorporation of sludge with soil and application of sludge before plant sprouting, will substantially reduce any plant exposure to VOCs.
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From page 109... ...
. L ~ FATE OF AND EXPOSURE TO TRACE ELEMENTS IN SLUDGE The availability of inorganic chemicals or trace elements for uptake by plants (and thus entry into the human food chain)
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Uptake of Trace Elements by Animals As with toxic organics, animals can be exposed to trace elements through sludge residuals adhering to plants, sludge on the soil surface or mixed into the soil, or trace elements absorbed and translocated by plants. All three routes can operate on grazing land, but only the third is relevant when animals are given feed grown on sludge-amended soils.
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From page 111... ...
Studies of the accumulation of trace elements in cattle grazed on sludge-amended pastures have revealed elevated levels in liver and kidney, but not in muscle tissue (Bertrand et al. 1981a, Baxter et al.
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concluded that the "ultimate" evaluation of health effects of reclaimed wastewater used for drinking water purposes must come from studies on whole animals. Furthermore, because of the difficulty of reliable interpretation of results of bioassay studies using single compounds isolated from wastewater, test animals should be exposed to concentrates of the whole reclaimed water.
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From page 113... ...
. SUMMARY A review of the literature for toxic organics and for inorganic trace elements in treated municipal wastewater effluents or treated sewage sludge indicates that most of these chemicals are either not transferred from soil to plant tissues or that transiocation to edible tissues does not reach levels harmful to consumers under normal agricultural conditions.
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1981a. Metal residues in tissue, animal performance, and carcass quality with beef steers grazing on Pensacola Bahiagrass pastures treated with liquid digested sludge.
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1985. Potential effects of sludge-borne heavy metals and toxic organics on soils, plants, and animals, and related regulatory guidelines.
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Land Application of Sewage Sludge, Vol. I-PB93-~1075; I=nd Application of Sewage Sludge, Vol.
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1983. Assessment of the Treatability of Toxic Organics by Overland Flow.
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1992. Statement by the National Food Processors Association on the Use of Treated Municipal Sewage Sludge in the production of crops for human consumption.
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1991. Bioavailability to plants of sludgeborne toxic organics.
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