Bioassays performed on the dilution series of the original soil samples
showed a dose response relationship in each series for only three
groups of organisms: earthworms (mortality),microorganisms (carbon
mineralization, dehydrogenase and phosphatase activity) and algae.
In these cases, L(E)C50 values were determined and the data are presented
in Table 6. By contrast, effects on plants and earthworm weight
revealed unusual ecotoxicity curves. Thus, soil S2 showed an inhibition
of earthworm weight of 57±1% at all concentrations tested, independent
of soil dilution (except at 100% where all individuals died and the
effects on weight could not be measured). Likewise, S2 showed wheat
and radish weight inhibitions of 63 ± 5 and 60 ± 4%, respectively, at
all dilutions tested and S3 only showed adverse effects on radishweight
at 25% of soil concentration. The unusual ecotoxicity curves in each
series may be due to the behavior of arsenic in soil, which is different
from cadmium, zinc or copper (Crouau and Pinelli, 2008),