Air Quality Criteria for Lead Volume II of II - (NEPIS)(EPA) - US ...

metal levels. Furthermore, although not significant, Pb levels in snails were higher when
tadpoles and sunfish extract were present than when only metals in the sediment were present.
Finally, snail predator avoidance was assessed. Snails (control and lead-exposed) were
stimulated with a predator indicator (i.e., crushed snails and an extract of crushed snail). Control
snails changed behaviors in the presence of the predator indicator, while exposed snails did not
alter their behavior. The authors suggested that metal exposure caused behavioral changes that
alter competitive interactions and the perception of predators by the snails. Thus, Pb may affect
the predator avoidance response of snails.
In further study, Lefcort et al. (2000) examined the predator avoidance behaviors of snails
and caddisflies. In separate experiments, the avoidance behavior of the snail, Physella
columbiana, and four caddisfly genera (Agrypnia, Hydropsyche, Arctopsyche, Neothremma)
were evaluated. The snails were collected from reference lakes and lakes downstream of the
Bunker Hill Superfund site. The snails from the affected lakes generally had higher cadmium,
Pb, and zinc tissue levels implying previous exposure to these metals. Snail predator avoidance
behavior was tested by exposure to crushed snail extract. Snails from the affected lakes did not
reduce their activity when exposed to the snail extract, implying a reduced predator avoidance.
The lack of response may make the snails at the affected lakes more prone to predation.
The caddisflies were evaluated at 36 sites from six different streams. As with the snails,
the caddisflies from the affected streams had higher cadmium, Pb and zinc tissue levels. The
time for caddisfly larvae to respond (i.e., how long immobile) to disturbance (i.e., lifted from
water for 3 seconds and moved to a new location) was evaluated. There was no correlation
between tissue metal level and any response variable (Lefcort et al., 2000). Therefore, the
authors concluded that preexposure to metals did not reduce predator avoidance for caddisflies.
Weber (1996) examined juvenile fathead minnows exposed to 0, 0.5, or 1.0 ppm Pb in
water during a 2-week preexposure and 2-week testing period (4 weeks total exposure). Feeding
behavior was evaluated by presenting two prey sizes (2-day-old and 7-day-old Daphnia magna).
Control fish began switching from larger, more difficult-to-capture 7-day-old daphnids to
smaller, easier-to-catch 2-day-old prey by day 3. Lead-exposed fish displayed significant
switching at day 3 (at 0.5 ppm) or day 10 (at 1.0 ppm). Thus, exposure to Pb delayed the altering
of prey size choices to less energetically costly prey.
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