Dose-Dependent Effects of Dietary Pb and Zn on Feeding and Growth Rates of the Landsnail Helix engaddensis

Dose-dependent effects of dietary lead and zinc on feeding and growth rates of adult Helix engaddensis snails were studied over a 1-month period followed by a 2-week recovery period. Snails were fed on an artificial diet containing the following lead or zinc CONCENTRATIONS= 0, 20, 100, 500, 2500, and 12,500 μg/g dry food. At the end of the 6 weeks, mortality rate among snails fed on Pb-contaminated diet was 18.3% (11/60) and the respective value for Zn-contaminated diet was 50% (30/60). Both metals significantly reduced growth and feeding rates. Snails were found to be sensitive to zinc but tolerant to lead. During the recovery period, snails fed on Zn-contaminated diet failed completely to feed or grow normally, whereas snails fed on Pb-contaminated diet showed signs of slow improvement in terms of feeding and growth rates. The NOEC and LOEC for lead were 100 and 500 μg·g−1, respectively, while the respective concentrations for zinc were 20 and 100 μg·g−1.