EFFECT OF ENVIRONMENTALLY RELEVANT CONCENTRATIONS OF SURFACTANTS ON THE DESORPTION OR BIODEGRADATION OF MODEL CONTAMINANTS IN SOIL

The protection of the terrestrial environment is becoming a major focu s for risk assessment, with discussions taking place tinder the aegis of both the OECD and rite EU. One area under discussion involves the d isposal of sludge from municipally operated sewage treatment plants to land for agricultural purposes, and the avoidance of possible problem s arising from the presence of surfactants in sludges used for this pu rpose. The laboratory experiments described here investigate the influ ence of environmentally relevant levels of surfactants on the sorption and biodegradation of other xenobiotic compounds present in sludge or soil. The influence of surfactants on the desorption of both an easil y desorbed compound, 2,4-dichlorophenoxyacetic acid (2,4-D), and a mor e difficult to desorb compound, alpha-napthol, is negligible for two c ontrasting soils. There is no detrimental effect on the biodegradabili ty of tither contaminant caused by LAS levels tip to eight times in ex cess of the levels normally found in the environment. Thus die potenti al of surfactant at levels present in sewage sludge to increase the en vironmental risk of other xenobiotic compounds also present in sludge or soil is extremely small. The relationship between experiments in th e laboratory and those carried out tinder realistic field conditions n eeds to be better understood, if laboratory tests are to be a useful b asis for realistic terrestrial risk assessment. Experiments such as di e ERASM-sponsored investigations by the Danish National Environmental Research Institute and the Danish Water Quality Institute on the deliv ery of linear alkylbenzene sulphonate (LAS) to Danish soil from sludge s produced under Danish conditions, on the bioavailability of LAS tind er these conditions, and on its toxicity to soil organisms, should inc rease the scientific understanding necessary to improve this laborator y-field relationship and to increase the scientific basis of terrestri al risk assessment.