Ref ID : 6125
Nicola A. Davies, Mark E. Hodson, and Stuart Black; The influence of time on lead toxicity and bioaccumulation determined by the OECD earthworm toxicity test. Environmental Pollution 121:55-61, 2003
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Internationally agreed standard protocols for assessing chemical toxicity of contaminants in soil to worms assume that the test soil does not need to equilibrate with the chemical to be tested prior to the addition of the test organisms and that the chemical will exert any toxic effect upon the test organism within 28 days. Three experiments were carried out to investigate these assumptions. The first experiment was a standard toxicity test where lead nitrate was added to a soil in solution to give a range of concentrations. The mortality of the worms and the concentration of lead in the survivors were determined. The LC50s for 14 and 28 days were 5311 and 5395 µg(Pb) g(soil)-1 respectively. The second experiment was a timed lead accumulation study with worms cultivated in soil containing either 3000 or 5000 µg(Pb) g(soil)-1. The concentration of lead in the worms was determined at various sampling times. Uptake at both concentrations was linear with time. Worms in the 5000 µg g-1 soil accumulated lead at a faster rate (3.16 µg(Pb) g(tissue)-1 day-1) than those in the 3000 µg g-1 soil (2.21 µg(Pb) g(tissue)-1 day-1). The third experiment was a timed experiment with worms cultivated in soil containing 7000 µg(Pb) g(soil)-1. Soil and lead nitrate solution were mixed and stored at 20 degrees C. Worms were added at various times over a 35-days period. The time to death increased from 23 hr, when worms were added directly after the lead was added to the soil, to 67 hr when worms were added after the soil had equilibrated with the lead for 35 days. In artificially Pb-amended soils the worms accumulate Pb over the duration of their exposure to the Pb. Thus time limited toxicity tests may be terminated before worm body load has reached a toxic level. This could result in under-estimates of the toxicity of Pb to worms. As the equilibration time of artificially amended Pb-bearing soils increases the bioavailability of Pb decreases. Thus addition of worms shortly after addition of Pb to soils may result in the over-estimate of Pb toxicity to worms. The current OECD acute worm toxicity test fails to take these two phenomena into account thereby reducing the environmental relevance of the contaminant toxicities it is used to calculate.