Chronic toxicity bioassay with ampularid snail Pomacea lineata (Spix 1824) (Mollusca: Prosobranchia)

Pomacea lineata (Spix, 1824), an extremely ubiquitous snail and pest to rice farmers throughout the orient, holds promise as a valuable resource for monitoring water quality in Northeast Brazil. In this paper, we present data to demonstrate its capacity as a test animal to consistently respond to low level herbicide concentrations (Paraquat and Roundup). Growth data to assess chronic toxicity, were generated in only 96 hours. Applying Duncan's test we were able to tentatively approximate a 96 and 192 hour no observed effective concentration (NOEC) and lowest observed effective concentration (LOEC) for Roundup of 1.0 and 2.0 and 0.5 and 1.0 mg/L, respectively (no acute toxicity was observed during 15 days of exposure.) No such estimates could be attempted with Paraquat, however, because every concentration tested was significantly different from the control percent increase in growth even at the lowest concentration tested (0.005 mg/L) there was an increase in growth that was significantly greater than control levels suggesting a hormetic effect.