The juvenile snails were purchased from a snail culturing farm
in Beijing, China and were selected from synchronous breeding to
ensure the same size, mass, and age. The snails were bred with
lettuce for 2 weeks in the same conditions as the toxicity test: temperature
(20 ± 0.5 C), moisture content (50% of the water holding
capacity). Two days before starting the test, the snails were woken
by spraying water, and the proportion of snails not woken was less
than 2%. The juvenile snails (4 weeks old) with a mean fresh mass
of 1.03 ± 0.10 g and a shell diameter of 16.50 ± 0.20 mm were
selected for all experiments.