Effects of copper (Cu2+), Zn (Zn2+), lead (Pb2+) and Cadmium (Cd2+) on the early development of freshwater snail, Radix quadrasi
2002
de Chavez, E.R.C. | de Lara, A.V. (Philippines Univ. Los Banos, College, Laguna (Philippines). Animal Biology Div.)
Heavy metals are one of the major toxic wastes being dumped into bodies of water. Irresponsible disposal of these chemicals causes detrimental effects on organisms living in the area. Mollusks, particularly gastropods, being slow moving could not easily escape or avoid stressed environments. They can bioconcentrate heavy metals in their tissues. Thus, they are considered as good indicators of heavy metal pollution. Most studies on heavy metals, however, deal with acute toxicity on the adults. The present study reports on the effects of four heavy metals (Cu2+, Zn2+, Pb2+ and Cd2+) on the early development of the common freshwater snail, Radix quadrasi. Trocophore larvae or 2-day old eggs of R. quadrasi were exposed to 0, 0.0001, 0.001, 0.01, 0.1 and 1.0 mg/L of Cu2+, Zn2+, Pb2+ and Cd2+ for 10 days, the period when all of the control snails would have hatched. A total of 54 egg masses, each contained 5060 eggs, were used. The eggs were placed in petri dishes filled with 30 ml of the test solution. For the control, aged tap water was used. There were three replicates for treatment and three egg masses were exposed to each concentration. The effects of the metals on the incubation period, percent hatching, growth and morphology of the developing snails were determined. Incubation period was delayed by two days in eggs exposed to lower concentrations (0.01-0.0001 mg/L) of Cu2+, Pb2+ and Cd2+. However, the incubation period of the zinc-treated eggs (0.01-0.0001 mg/L) lasted for 10 days, which did not differ significantly from the control with 9 days incubation. Among treated eggs, percent hatching was highest in 0.0001 mg Zn2+/L (15.56) and lowest in 0.01 mg Cu2+/L (0.85). None of those exposed to higher dosages (0.1 and 1.0 mg/L) hatched. Occurrence of morphological abnormalities and growth retardation were also dose dependent. The present study suggests that R. quadrasi is a potential bioindicator of heavy metal contamination in freshwater ecosystem
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