Acute and sub-lethal toxicity of landfill leachate towards two macro-invertebrates

Aspecific leachate that contained 1.036 mgl^–1 of 2-chlorobiphenyl was used in the study (255 mgl^–1 COD and 133 mgl^–1 BOD5). When operated on a 10 day hydraulic retention time (RT), reed beds planted with Juncus effusus removed 60% of the leachates COD, compared to 25% in unplanted beds. The constructed wetlands proved effective at reducing the level of acute toxicity to A. aquaticus and G. pulex. In untreated leachate, the LC₅₀ for A. aquaticus was 57% v/v leachate in deionized water and 5% for G. pulex. When reed beds were operated on a 1–10 day RT, the LC₅₀ for Asellus increased from 69% to below the LC50 threshold. The Gammarus LC₅₀ also rose from 10% to 50%. The maximum toxicity reduction achieved by unplanted beds was 10% towards A. aquaticus and 5% for G. pulex, when operated on a 10 day RT. However, in sub-lethal concentrations of reed bed effluent (100%, 80% and 60% dilutions, obtained from planted beds on a 10 day RT), the final length of Asellus was significantly reduced, in comparison to a deionized water control. It is also speculated that chronic leachate stress may have affected the fecundity of Gammarus, however, insufficient data was collected to statistically validate this hypothesis.