George A. O'Connor

Plant uptake of non-ionic organic chemicals from soils

Methodologies utilizing simple properties of chemicals - half-life (T1/2), log octanol-water partition coefficient (log Kow) and Henerys Law constant (Hc) - are developed to screen organic chemicals for potential plant uptake.

Organic compounds in sludge-amended soils and their potential for uptake by crop plants.

Numerous toxic organic chemicals (TOs), with a wide range of chemical properties, can occur in sewage sludges. The vast majority of sludge-borne TOs occur at low concentrations, and even lower TO concentrations are expected in sludge-amended soils. Further, most TOs are so strongly reactive in the soil-sludge matrix that their bioavailabilities to plants are expected to be low. A host of experimental techniques have been employed to measure TO plant uptake and to relate bioavailability to TO chemical and physical properties. The strengths and weaknesses of several experimental approaches are examined, and the resulting data are evaluated. Sound experimental data, especially field data and/or data from studies with endogenously sludge-borne TOs, indicate negligible contamination of crop plants with TOs in sludge-amended soils. Assessing the potential for plant uptake of sludge-borne TOs involves determining: (a) which TOs are most likely present in biosolids and what are their toxicities; (b) what quantities of TOs are likely to be added to the growth media via biosolids application; (c) what effects various dissipation/dispersion reactions have on the potential bioavailability of TOs; and (d) what are the various mechanisms for plant uptake/metabolism of TOs.

Degraded water reuse: an overview.

Communities around the world face increasingly severe fresh water supply shortages, largely due to expanding populations and associated food supply, economic development, and health issues. Intentional reuse of degraded waters (e.g., wastewater effluents, irrigation return flows, concentrated animal feeding operations [CAFO] effluents, stormwater, and graywater) as substitutes for fresh waters could be one solution to the challenge. We describe the various degraded water types and reuse options and limitations and restrictions to their use. Emphasis is given to reuse scenarios involving degraded water applications to soil. The potential for degraded water reuse is enormous, but significant barriers exist to widespread adoption. Barriers include research questions (some addressable by traditional soil science approaches, but others requiring novel techniques and advanced instrumentation), the lack of unifying national regulations, and public acceptance. Educational programs, based on hard science developed from long-term field studies, are imperative to convince the public and elected officials of the wisdom and safety of reusing degraded waters.

Efficacy of drinking-water treatment residual in controlling off-site phosphorus losses: a field study in Florida.

Land application of drinking-water treatment residuals (WTR) has been shown to control excess soil soluble P and can reduce off-site P losses to surface and ground water. To our knowledge, no field study has directly evaluated the impacts of land application of WTRs on ground water quality. We monitored the effects of three organic sources of P (poultry manure, Boca Raton biosolids, Pompano biosolids) or triple superphosphate co-applied with an aluminum-based WTR (Al-WTR) on soil and ground water P and Al concentrations under natural field conditions for 20 mo in a soil with limited P sorption capacity. The P sources were applied at two rates (based on P or nitrogen [N] requirement of bahiagrass) with or without Al-WTR amendment and replicated three times. Without WTR application, applied P sources increased surface soil soluble P concentrations regardless of the P source or application rate. Co-applying the P sources with Al-WTR prevented increases in surface soil soluble P concentrations and reduced P losses to shallow ground water. Total dissolved P and orthophosphate concentrations of shallow well ground water of the N-based treatments were greater (>0.9 and 0.3 mg L(-1), respectively) in the absence than in the presence ( approximately 0.6 and 0.2 mg L(-1), respectively) of Al-WTR. The P-based application rate did not increase ground water P concentrations relative to background concentrations. Notwithstanding, Al-WTR amendment decreased ground water P concentrations from soil receiving treatments with P-based application rates. Ground water total dissolved Al concentrations were unaffected by soil Al-WTR application. We conclude that, at least for the study period, Al-WTR can be safely used to reduce P leaching into ground water without increasing the Al concentration of ground water.

Organic contaminants in municipal biosolids: risk assessment, quantitative pathways analysis, and current research priorities

Abstract Basic research and monitoring of the fate and potential effects of PCBs and other xenobiotic organics in biosolids (municipal sewage sludge) used on cropland have identified specific Pathways by which the xenobiotic organics in biosolids can reach and cause exposure to humans, livestock, plants, soil biota, wildlife, etc. In order to provide the scientific basis for the Clean Water Act Regulations (40 CFR 503) on land application of biosolids in the U.S., a Pathway Approach to risk assessment was undertaken. Pathways included general food production; garden food production; soil ingestion by humans, livestock, and wildlife; human exposure through livestock tissues where the livestock were exposed through crop contamination or biosolids/soil ingestion; wildlife exposure through soil organisms; release to surface and groundwater; volatilization into inhaled air, or dust generated by tillage. Two Pathways were found to comprise the greatest risk from persistent lipophilic organic compounds such as PCBs: (1) adherence of biosolids to forage/pasture crops from surface application of fluid biosolids, followed by grazing and ingestion of biosolids by livestock used as human food; and (2) direct ingestion of biosolids by children. Each Pathway considers risk to Highly Exposed Individuals (HEIs) rather than to the general population who seldom have appreciable exposure to biosolids or foods grown on biosolid-amended soils. Because present (1995) biosolids contain very low levels of PCBs in countries which have prohibited manufacture and use of these compounds, the estimated increase in lifetime cancer risk to HEIs from biosolids-borne PCBs applied to cropland or gardens was much less than 10 −4 . Low biosolids PCBs and low probability of simultaneously meeting all the constraints of the HEI indicate that HEIs have less than 10 −7 increase in lifetime cancer risk from biosolids-borne PCBs; this provides even higher protection to the general population. We conclude that quantitative risk assessment for potentially toxic constituents in biosolids can be meaningfully conducted because research has provided transfer coefficients from biosolids and biosolid-amended soils to plants and animals needed to assess risk for many organic compounds.

Effects of pasture‐applied biosolids on forage and soil concentrations over a grazing season in north Florida. II. microminerals

Abstract The experiment rationale was to determine forage micromineral concentrations as effected by biosolids fertilization. We determined the effects of two exceptional quality biosolids on bahiagrass trace mineral concentrations as related to beef cattle requirements. Twenty‐five 0.8‐ha pastures were divided into five blocks. Two biosolids were applied as normal and double agronomic rates. The control received NH4NO3. Forages were analyzed for total copper (Cu), iron (Fe), manganese (Mn), zinc (Zn), molybdenum (Mo), cobalt (Co), and selenium (Se), and soils were analyzed for Mehlich I extractable Cu, Mn, and Zn. Some significant increases (P<0.05) in forage Co, Cu, Fe, Zn, and Se were observed at various sampling times, but the increases were generally small and biologically insignificant. Although forage Mo samples from pastures with the Tampa biosolids applied were consistently higher than the control (P<0.05), at no time did they approach levels considered toxic. Similar results were seen in forage Mn concentrations, with treatment Baltimore‐2X elevating (P<0.05) Mn concentrations as well. Deficiencies of Co, Cu, Zn, and Se are common in this Florida region and slight elevations due to biosolids treatment could be beneficial. Biosolids applied at the highest rates improved soil Cu and Zn concentrations above control soils and soil Mn was increased over the control at both sampling times for Baltimore‐2X. In relation to beef cattle requirements, the majority of forages were deficient in Co, Cu, Se, and Zn. In summary, biosolids fertilization slightly improved the micromineral status of forage and soil, without creating toxicity.

Retention‐release characteristics of triclocarban and triclosan in biosolids, soils, and biosolids‐amended soils

Transport models that incorporate retention/release characteristics of organic compounds in soils and sediments typically assume that organic-carbon normalized partition coefficients (K(OC)) apply to all solid matrices and that the partitioning process is completely reversible. Partition coefficients (K(d)) (from which the K(OC) was calculated), and retention/release characteristics of triclocarban (TCC) and triclosan (TCS) in biosolids, soils, and biosolids-amended soils were determined. Four soils of different physicochemical properties amended with biosolids at 10 g/kg, together with unamended soils, and several biosolids were separately spiked with either [(14)C]TCC or [(14)C]TCS for the various determinations. The hysteresis coefficient values of the two compounds were consistently <1 in all three solid matrices, suggesting strong hysteresis. Multiple desorption steps (24 h each) over several days revealed incomplete desorption of the two compounds from all three solid matrices. The K(d) values determined in biosolids (log K(d) 3.34 +/- 0.13 for TCC and 3.76 +/- 0.39 for TCS) were greater than those determined in soils (log K(d) 1.71 +/- 0.09 for TCC and 2.25 +/- 0.26 for TCS) and biosolids-amended soils (log K(d)1.90 +/- 0.16 for TCC and 2.31 +/- 0.19 for TCS), however, the K(OC) values of all three solid matrices were similar (log K(OC) of 3.82 +/- 0.16 for TCC and 4.26 +/- 0.31 for TCS). Thus, it was concluded that a single or a narrow range of K(OC) values for TCC and TCS may be appropriate to describe retention of the compounds in soils and sediments. However, models that assume complete reversibility of the retention/release processes of the compounds in soils and sediments may not adequately describe the retention/release characteristics of the compounds in soils and sediments, especially when the chemicals are biosolids borne.

Toxicity and bioaccumulation of biosolids-borne triclosan in food crops

Triclosan (TCS) is an antimicrobial compound commonly found in biosolids. Thus, plants grown in biosolids-amended soil may be exposed to TCS. We evaluated the plant toxicity and accumulation potential of biosolids-borne TCS in two vegetables (lettuce and radish) and a pasture grass (bahia grass). Vegetables were grown in growth chambers and grass in a greenhouse. Biosolids-amended soil had TCS concentrations of 0.99, 5.9, and 11 mg/kg amended soil. These TCS concentrations represent typical biosolids containing concentrations of 16 mg TCS/kg applied at agronomic rates for 6 to 70 consecutive years, assuming no TCS loss. Plant yields (dry wt) were not reduced at any TCS concentration and the no observed effect concentration was 11 mg TCS/kg soil for all plants. Significantly greater TCS accumulated in the below-ground biomass than in the above-ground biomass. The average bioaccumulation factors (BAFs) were 0.43 ± 0.38 in radish root, 0.04 ± 0.04 in lettuce leaves, 0.004 ± 0.002 in radish leaves, and <0.001 in bahia grass. Soybean (grain) and corn (leaves) grown in our previous field study where soil TCS concentrations were lower (0.04-0.1 mg/kg) had BAF values of 0.06 to 0.16. Based on the data, we suggest a conservative first approximate BAF value of 0.4 for risk assessment in plants.

Bioavailability to Plants of Sludge-Borne Toxic Organics

Land application is an efficient and cost-effective method of sludge disposal that also recycles essential nutrients to the soil. Sludge additions can also improve the physical and chemical properties of soil, albeit at high initial or cumulative application rates. Thus, land application of sludge in the agricultural sector is responsive to the policy of U.S. EPA (40 CFR 503, 1989) of promoting beneficial use of sewage sludge. Concern about the environmental fate of toxic organic (TOs) that can occur in sludges, however, threatens routine use of the practice.

Toxicity and bioaccumulation of biosolids-borne triclosan in terrestrial organisms

Triclosan (TCS) is a common constituent of personal care products and is frequently present in biosolids. Application of biosolids to land transfers significant amounts of TCS to soils. Because TCS is an antimicrobial and is toxic to some aquatic organisms, concern has arisen that TCS may adversely affect soil organisms. The objective of the present study was to investigate the toxicity and bioaccumulation potential of biosolids-borne TCS in terrestrial micro- and macro-organisms (earthworms). Studies were conducted in two biosolids-amended soils (sand, silty clay loam), following U.S. Environmental Protection Agency (U.S. EPA) guidelines. At the concentrations tested herein, microbial toxicity tests suggested no adverse effects of TCS on microbial respiration, ammonification, and nitrification. The no observed effect concentration for TCS for microbial processes was 10 mg/kg soil. Earthworm subchronic toxicity tests showed that biosolids-borne TCS was not toxic to earthworms at the concentrations tested herein. The estimated TCS earthworm lethal concentration (LC50) was greater than 1 mg/kg soil. Greater TCS accumulation was observed in earthworms incubated in a silty clay loam soil (bioaccumulation factor [BAF] = 12 ± 3.1) than in a sand (BAF = 6.5 ± 0.84). Field-collected earthworms had a significantly smaller BAF value (4.3 ± 0.7) than our laboratory values (6.5-12.0). The BAF values varied significantly with exposure conditions (e.g., soil characteristics, laboratory vs field conditions); however, a value of 10 represents a reasonable first approximation for risk assessment purposes.