Ecotoxicological assessment of the impact of fluoride (F-) and turbidity on the freshwater snail Physella acuta in a polluted river receiving an industrial effluent.

We carried out field studies and laboratory experiments to assess the impact of fluoride (F-) and turbidity on the freshwater snail Physella acuta in a polluted river receiving an industrial effluent (the middle Duraton River, Central Spain). Fluoride concentrations and turbidity levels significantly increased downstream from the industrial effluent (with the highest values being 0.6 mg F-/L and 55.2 nephelometric turbidity unit). In addition, higher deposition of fine inorganic matter was evident at polluted sampling sites. Conversely, the abundance of P. acuta significantly declined (until its virtual disappearance) downstream from the industrial effluent. Toxicity bioassays showed that P. acuta is a relatively tolerant invertebrate species to fluoride toxicity, with estimated safe concentrations (expressed as LC0.10 values for infinite hours of exposure) for juvenile and adult snails being 2.4 and 3.7 mg F-/L, respectively. Furthermore, juvenile snails (more sensitive than adult snails) did not show significant alterations in their behavior through 15 days of exposure to 2.6 mg F-/L: mean values of the proportion of test snails located on the water surface habitat, as well as mean values of the sliding movement rate (velocity) of test snails, never showed significant differences when comparing control and treatment glass vessels. It is concluded that instream habitat degradation, derived from increased turbidity levels, might be a major cause for significant reductions in the abundance of P. acuta downstream from the industrial effluent. The presence of the competing gastropod Ancylus fluviatilis could also affect negatively the recovery of P. acuta abundance.