Researching Ecological Effects Of Inorganic Fluoride On Aquatic Ecosystem

The massive use of hydrofluoric acid by the photovoltaic manufacturing industry in manufacturing high-purity polysilicon, silicon wafer and PV cell & module introduced a lot of inorganic fluorides into its surrounding water. The increasing levels of inorganic fluoride in the aquatic environments is a matter of concern for freshwater ecosystems.Although data on fluoride toxicity to human beings are increasing in the scientific literature, few data are available regarding the effects on aquatic organisms. Therefore,this paper was undertaken to investigate the ecological effect of inorganic fluoride on the aquatic organism included microorganism, acquatic animal and plants by the means of laboratoy culture and simulation experiments. The main results are as follows.In order to investigate the influence of fluoride-polluted water discharge on the receiving water, effects of fluoride on bacterial community in aquatic microcosms were evaluated. The kinetics of the change of number of dominant bacteria species induced by exposure of fluorides was observed by colony counting method. The results showed that fluoride exerts diverse bacterial effects in a time-, concentration-, and bacteria-species-dependent manner. Appropriate concentration of fluoride( ≦ 1mg/L)could remarkably promoted the growth of microorganism in water phase and sediment.However, in high concentration of fluoride treatment(>10mg/L), it was found that the relative counts of microorganism decreased gradually with the exposure concentration and exposure time. Of all the five biogeochemical cycling bacteria, sulfur oxidizing bacteria was most sensitive to fluoride, can be used as a potential microbial ecological receptor for assessing environmentally ecological effect of inorganic fluoride. Among the test groups, reductions were minimal in the cellulose-decomposing bacteria populations, indicating that cellulose-decomposing bacteria had greater potential for fluoride resistance.In the acute study of fluoride, it was found that fluoride application to the Bellamya aeruginosa resulted in an overall no observable adverse effect of 1 mg/L after 96 hours.But the behavioral alteration of Bellamya aeruginosa exposed to high concentration of fluoride( ≥ 10mg/L) was observed. The adverse reaction of Bellamya aeruginosa exposed to fluoride had clear concentration- and time-dependent effects(p < 0.05). The48, 72 and 96 hours LC50 of fluoride in Bellamya aeruginosa were 233.55, 81.04 and34.99mg/L, respectively. And the safe concentration of fluoride in water for Bellamya aeruginosa was 3.50mg/L.A 40-day growth trial in semi-static acquatic microcosm was conducted to determine the reproduction, growth inhibition and accumulation of fluoride to Bellamya aeruginosa. Comparing to the control, newly born Bellamya aeruginosa growth was inhibited significantly when exposed to 135 and 270 mg F-/kg(p < 0.05). Meanwhile,the reproduction of adult Bellamya aeruginosa was inhibited as well. Fluoride accumulated in Bellamya aeruginosa increased with the exposure concentration and time. The type of tissue is an important biotic factor affecting fluoride bioaccumulation in Bellamya aeruginosa, with the shell accumulating more fluoride than the soft tissue;the developmental stage seems to be another important biotic factor affecting fluoride bioaccumulation in Bellamya aeruginosa, with juveniles being able to accumulate fluoride more rapidly than adults exposed to high concentration of fluoride.Three typical acquatic plants that widely distributed in China were chosen as test plants to study the effects of fluoride. Fluoride toxicity to aquatic plants increased with increasing fluoride concentration, leading to reducing of total plants biomass. Fluoride can either inhibit or enhance the height of Callitriche stagnalis Scop., depending upon the concentration of fluoride. Besides, the tolerability of three typical acquatic plants to fluoride showed the following order: Najas graminea Del.>Callitriche stagnalis Scop.> Potamogeton distinctus A Benn.. Similarly, the fluoride accumulation in aquatic plants increases with increasing level of fluoride treatment. The order of accumulation of fluoride in Callitriche stagnalis Scop. found to be leaf < stem < root. The bioaccumulation coefficients of fluoride of three plants were all larger than 1.Furthermore, the cumulation ability of Najas graminea Del.was significantly stronger than that of Callitriche stagnalis Scop., while Potamogeton distinctus A Benn. showed superior cumulation ability.