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Earthworms' uptake of persistent organic pollutants from sewage sludge
Anja Klann, Jessica Toft and Ole von Uexkull Supervisor: Arnout ter Schure Department of Ecology, University of Lund, SE-223 62 Lund, Sweden
Sludge from wastewater treatment plants (WWTPs) has been commonly used as fertiliser in agriculture during the last four decades. Besides phosphorus and nitrogen the sludge contains relatively high levels of heavy metals and persistent organic pollutants (POPs). Using sludge in this manner therefore involves a risk of bioaccumulation of such compounds in organisms; This experiment was conducted to determine the uptake of several POPs in earthworm (Eisenia fetida). Sewage sludge from a WWTP in Landskrona served as source for POPs. Compost soil including earthworms was taken from a compost-heap. To obtain measurable levels within a short period of time, more sludge was applied to the compost soil than under natural conditions.
Earthworms were kept in six buckets in total; three of them contained compost soil and three contained a mixture of sewage sludge and compost soil in the ratio of one to two (w/w l:2). Samples consisted of ten earthworms and were taken before the experiment (t = 0 weeks), after two weeks (t = 2 weeks) and four weeks (t = 4 weeks). Soil samples of about 5g each were taken before the experiment was initiated (t = 0).
The fat of earthworms containing POPs was extracted with an acetone/cyclohexane mixture. The extract was cleaned with concentrated sulphuric acid. The soil samples were analysed for water content, organic matter and POPs and extracted in a similar manner. All the samples were analysed with GC/ECD. PCBs congeners 138, 153, 170, PBDE congeners 47, 99, l53 and several pesticides were identified in both soil samples and earthworms.
The results show an uptake of the detected compounds over time. Since the experiment was undertaken in a short period of time, no steady state was reached. Sludge mixture contained more of the compounds analysed than the compost soil. Subsequently the uptake of compounds in earthworms exposed to sludge was higher compared to uptake of earthworms exposed to compost soil. Even though we applied more sludge than under natural circumstances, we conclude that sludge should not be considered a suitable fertiliser due to the high levels of POPs and their bioaccumulation into earthworms.