Population dynamics in Asellus aquaticus as modified by chronic leachate stress

In the past, many landfill sites were constructed and operated without engineering containment, and from which leachate is likely to arise over the next several decades. Landfill leachate can contain high concentrations of toxic substances, which may pose a threat to the surroundings. In the worst cases, leachates may seep through the underlying substrata causing contamination of groundwater, of surface water drains, and ultimately of the rivers into which they discharge. As a consequence, the diversity and species richness of benthic communities are often degraded. 

The chronic toxicity of a landfill leachate was investigated in this study, with respect to determining the 'environmentally safe' concentration in which the long term survival of an Asellus aquaticus population is assured. The leachate was from a disused site known to contain industrial wastes, and samples were collected from a surface drain. The leachate used in the toxicity tests had a 600 mgl^-1 BOD and 1200 mgl ^-1 COD. 

Sub-lethal toxicity tests were carried out at concentrations that were lower than the acute toxicity threshold of Asellus aquaticus. The toxicity was judged on the basis of offspring produced and the growth rate of newly born individuals. Tests showed that even a dilution of 1:20 would affect the size of the breeding colony of Asellus. A 30 mgl^-1 COD concentration was judged to be the 'environmentally safe' leachate dilution in which the number of offspring, birth frequency and juvenile length would not be affected. At this concentration the integrity of an Asellus population would be protected.