ORGANIC CHEMICALS ENTERING AGRICULTURAL SOILS IN SEWAGE SLUDGES: SCREENING FOR THEIR POTENTIAL TO TRANSFER TO CROP PLANTS AND LIVESTOCK
Report No FR0169
K C Jones* and S R Wild* * Institute of Environmental and Biological Sciences, Lancaster University
To review the occurrence of organic contaminants in sewage sludge. To evaluate, using known physico-chemical properties, the potential for significant organic contaminants to transfer to the human food-chain by plant and animal accumulation from sewage sludge applied to agricultural land. To identify the inadequacies of existing information.
The occurrence and fate of organic contaminants in sewage sludge are largely unknown. Amid such uncertainty, public concern has threatened the security of the agricultural disposal route for sludge in several European countries.
By using physico-chemical data, the likely behaviour and propensity of organic contaminants to transfer in sludge-amended agroecosystems can be evaluated. This provides a more focused approach than 'priority pollutant' lists and 'hazard rankings' commonly used for drinking and waste waters. This more scientifically-based methodology to identifying appropriate experimental studies and pathway analyses now needs to be combined with more detailed information on the occurrence and concentrations of organic contaminants in sludge.
V RESUME OF CONTENTS
Many different organic compounds are present in sewage sludges, arising from industrial, domestic and atmospheric inputs to wastewaters. The likely fate and behaviour of these compounds during wastewater treatment, and their occurrence in sewage sludges is discussed. The environmental fate and behaviour of organic compounds can be assessed from a knowledge of their physico-chemical properties. The behaviour of organic compounds in soils, and their potential to transfer to plants and livestock is discussed and certain general principles which control chemical behaviour are highlighted. A database of key physico-chemical properties for over 100 'priority' chemicals known to occur in sewage sludges is compiled. Aqueous solubility, the octanol: water partition coefficient, the Henry's Law constant and likely biodegradation are included because they are important properties which control organic compound behaviour. Compound behaviour in soil is evaluated by assessing the potential to adsorb, volatilise, leach to groundwater and resist degradation. Potential transfers to plants are also assessed by considering separately the propensity for compound retention by root surfaces; root uptake and translocation; and foliar uptake. Transfers to livestock by soil and herbage ingestion, and the propensity to bioconcentrate in livestock tissues and milk are also evaluated. Clear differences between and within defined groups of compounds emerge from the screening procedure and different types of compound behaviour are highlighted. Importantly, the screening principles established here can be readily applied to other compounds which have not been considered to date. A number of specific recommendations are made for further literature-based, and experimentally-based, studies.
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