EU Consultants Report Ignores Science on LAS Sludge Safety
A recently released consultants report prepared for the European Commission (“Pollutants in urban waste water and sewage sludge”) ignores the extensive scientific information available on LAS. Both laboratory and real world monitoring data demonstrate that LAS poses no risk to the terrestrial environment when sewage sludge containing LAS is applied to soil as a fertilizer, a common practice in Europe and North America. The report acknowledges that residual levels of LAS in sludge applied to soil rapidly biodegrade to insignificant levels and that the highest LAS levels in soil are hundreds of times lower than levels that would harm crop plants. Instead of relying on these findings, or examining the extensive additional science available, the report accepts without questioning what we believe to be a politically driven position taken on the draft revised EU sludge directive. This position, which the report was apparently intended to support, proposes that sludge having LAS levels higher that an arbitrarily chosen value (2600 mg/kg dry weight) should not be used for agricultural purposes.
Because this policy is clearly not based on science, unfortunate implications can be foreseen. Since levels of LAS in sewage sludge are typically higher than the cut-off limit, the proposal will prevent the use of sludge on agricultural land, leading to additional public costs to incinerate or landfill sludge with no benefit to the environment.
Additional information on the environmental safety of LAS, including the safety of the residual levels of LAS present in sewage sludge, can be found on this site.
Further information on LAS removal during sewage treatment, the use of sewage sludge as fertilizer and the environmental safety of LAS in sewage sludge is provided below.
LAS Removal in Sewage Treatment
Laundry detergents and other cleaning products contain LAS as the major cleaning agent, or surfactant. In Europe and North America, laundry detergents are discharged to pubic sewers and the wastewater is treated in sewage treatment plants. Modern treatment plants employ aerobic conditions and the microorganisms present in sewage (“activated sludge”) to kill disease-causing microorganisms that might be present and to rapidly biodegrade the organic materials present. In the case of LAS, greater than 99% of the LAS present in the sewage is removed during the treatment process.
Use of Sewage Sludge as Fertilizer
Growth of the microorganisms during sewage treatment leads to excess biosolids or sludge, which contains residual levels of LAS. This excess sludge is then subjected to either anaerobic or aerobic treatment to reduce the levels of solids. The remaining sludge is either applied to agricultural fields as fertilizer or incinerated or placed in landfills. Of these options, the use of sludge as fertilizer is the environmentally preferred disposal option because the nutrients present in the sludge are recycled back to the soil.
Environmental Safety of LAS in Sewage Sludge
It has been known for many years that the LAS and other common substances present in sewage sludge, such as soap, are not extensively reduced during anaerobic sludge treatment. The reason for the lack of removal is unclear since LAS has recently been shown to undergo anaerobic biodegradation (THE CLER REVIEW, vol. 6, 2000). Nonetheless, when sludge is applied to soil as a fertilizer, LAS undergoes rapid biodegradation so that LAS levels in the soil rapidly decrease. Even the highest levels of LAS present in sludge, the initial levels at the time of sludge application, pose no risk to the organisms present in the soil or to plant crops.
A recent review of the environmental safety of LAS in sludge applied to soil (L. Cavalli and L. Valtorta, Tenside Surf. Det., vol. 36, pages 22-28, 1999) was published in THE CLER REVIEW, vol. 5, 1999. Additional studies on this topic were presented at a scientific conference in Copenhagen in April 1999. Extended summaries of two studies and a report of the conference are also published in vol. 5 of THE CLER REVIEW.
The key studies from the Copenhagen conference have now been published (Environmental Toxicology and Chemistry, vol. 20, pages 1656-1697, 2001). These studies, and more of the other latest research on LAS, will appear in the 2002 issue of THE CLER REVIEW.