April 2003

STUDY DEMONSTRATING SAFETY OF LAS IN SLUDGE-AMENDED SOILS TO BE PRESENTED AT BIOSOLIDS CONFERENCE

(Trondeim, Norway) – The agricultural use of sludge (biosolids) containing residual levels of linear alkylbenzene sulfonate (LAS) from sewage treatment is an environmentally-safe method to fertilize soils in Western Europe, according to a study to be presented at a major Norwegian biosolids conference in June 2003.

The study will conclude that LAS, a cleaning agent (surfactant) used widely in laundry detergents, does not present an ecological risk when present in sludge applied to agricultural soils. Residual levels of LAS become associated with sludge during sewage treatment and remain with the sludge after treatment. Fertilizing agricultural soils with sludge – which is rich in nutrients – has long been recognized as an environmentally safe method for increasing farm yields and conditioning soils.

The research to be presented in Norway concludes that only scenarios that involve “worst-case” conditions, i.e. extremely frequent sludge applications, or extremely slow biodegradation situations in areas with very hard water conditions, may require risk management to deal with residual levels of LAS in the sludge. These could include alternative methods of sludge disposal or a modification in the rate of sludge application.

To draw this conclusion, a team of European academic, industry and government scientists examined real-life scenarios involving agricultural sludge application and compared them to the extensive body of research available on the environmental safety of LAS, including ecotoxicological data on invertebrates and plants. The research team determined that typical levels of LAS present in sludge were well below levels likely to cause ecological harm. The team used risk assessment methodologies developed by soil specialists at the International Life Scientists Institute (ILSI), which take into account the potential for plant uptake, groundwater leaching, run-off from surface erosion, human health exposure via drinking water, plant consumption and soil ingestion.

The study was conducted by the ILSI European Sludge Risk Assessment Group. It will be presented at the International Water Association (IWA) Biosolids Conference 2003, to be held in at the Norwegian University of Science and Technology in Trondeim, Norway on June 23-25.

More information about the conference can be found at the IWA Biosolids 2003 Conference web site at http://www.ivt.ntnu.no/ivm/Biosolids2003.