TERRESTRIAL RISK ASSESSMENT FOR LINEAR ALKYL BENZENE SULFONATE (LAS) IN SLUDGE-AMENDED SOILS

A comparison of the estimated environmental concentration and the effe ct concentrations (in the laboratory or field) in the receiving compar tment form the basis of environmental risk assessments. This paper rev iews processes that critically influence the fate of LAS in the terres trial environment. Concentrations of LAS in sludge are quite high due to sorption to primary sludge, precipitation of Ca and Mg-salts of LAS , and lack of biodegradation under anaerobic digestion. This implies t hat when sludge is applied to soil e.g. as a fertilizer, considerable amounts of this important surfactant may enter the terrestrial environ ment. Influence of aerobic situations on LAS concentrations during slu dge storage needs further research to allow incorporation into the ris k assessment. Aerobic biodegradation in soil is considered the most im portant removal mechanism of LAS loading to the terrestrial environmen t through sludge-amendment. Sorption plays a role in determining the r esidence time of a chemical in the soil, hereby enabling more time for biodegradation to occur. In addition, sorption may affect the express ion of effects of surfactants towards benthic and soil dwelling organi sms and plants. Another factor that needs further attention is the for m of LAS in the environment, which is not similar to the commercial ma terial applied in detergents. The differential sorption and biodegrada tion of the LAS components lead to a shift in the alkyl chain length ( homologue), and phenyl-isomer distribution towards increased hydrophob icity. Also, occurrence of Ca/Mg-salts in the environment versus the N a-salt for the commercial material critically impacts the extrapolatio n of effects data obtained in lab studies (mostly performed with the c ommercial material) to the field. The literature data were used in com bination with strategies and methods provided by the European Union Te chnical Guidance Document in support of risk assessment of new and not ified substances (1996) for the prediction of environmental concentrat ions of LAS entering the soil system through sludge applications. Soil biodegradation is an essential, necessary element for the PEG-calcula tions of LAS. The initial realistic worst case assessment presented in dicates no human health risks exists with indirect exposure to LAS thr ough either food or drinking water. Also, current LAS use does not pos e a risk to terrestrial organisms such as plants and invertebrates. (C ) 1998 Elsevier Science Ltd.