Uptake and accumulation of pentachlorophenol and sodium pentachlorophenate by earthworms from water and soil

Toxicity values were obtained for pentachlorophenol (PCP) and other compounds in the standard OECD and EEC earthworm test. To help explain the uptake and bioaccumulation mechanisms of PCP which affect toxicity, experiments have been conducted using the earthworm Allolobophora caliginosa. The experiments showed that radiolabelled PCP and its sodium salt, PCP-Na, were taken up rapidly by the earthworms during 24 h from aqueous solution (1 and 10 micrograms ml-1) in a limited volume (5 ml) to give a bioconcentration factor (BCF) of 2.5, and that the solution concentration had no apparent influence on uptake. Exposure of worms over a period of 14 days in a large volume of soil under laboratory conditions increased the BCF, which was approximately 8 and 13 in the low (2.2 mg g-1 soil) and high (11.2 mg g-1 soil) soil concentration respectively. Longer exposures of the same worm species for 131 days in another soil type, in lysimeters under outdoor conditions, did not increase the BCF beyond that reached after 14 days exposure in the artificial soil. There were differences between earthworm species in their bioconcentration ability: Lumbricus terrestris accumulated 3 times more radiocarbon than A. caliginosa. Irrespective of the concentrations in solution, the binding of free phenol (PCP) in worm tissues was greater than for its sodium salt (PCP-Na), but there were no apparent differences in the amount of these substances eliminated, which was rather low. Metabolic studies have shown that PCP is metabolised more rapidly than PCP-Na in the worms body, resulting in the formation of metabolites which are polar in nature and also probably of conjugates. The results are discussed in relation to the mechanisms which may be responsible for the detoxification of PCP in earthworms.