Contaminated sediment in the Detroit River provokes acclimated responses in wild brown bullhead (Ameiurus nebulosus) populations

In a previous study, adaptive responses to a single polycyclic aromatic
hydrocarbon (PAH), benzo[a]pyrene (BaP), were identified in brown bullhead
(Ameiurus nebulosus) captured from contaminated sites across the Great
Lakes. The tumor suppressor p53 and phase I toxin metabolizing CYP1A genes
showed a protective and refractory response, respectively, up to the F1
generation (Williams and Hubberstey, 2014). As an extension to the first
study, bullhead were exposed to sediment collected from sites along the
Detroit River to see if these adaptive responses are attainable when fish
from a contaminated site are exposed to a mixture of contaminants, instead
of a single compound. p53 and CYP1A proteins were measured in both studies
with the addition of phase II glutathione-s-transferase (GST) activity in
the second. Three treatment groups were measured: acute (treated
immediately), cleared (depurated for three months and subsequent
treatment), and farm raised F1 offspring. All three treatment groups were
exposed to clean and contaminated sediment for 24 and 96 hours. Acute fish
from contaminated sites exposed to contaminated sediment revealed an
initial elevated p53 response that was not reached in cleared fish exposed
to contaminated sediment. Instead, cleared and F1 bullhead from clean and
contaminated sites had overlapping p53 expression patterns in response to
contaminated sediment by 96 hours. Acute fish from contaminated sites
exposed to contaminated sediment revealed refractory CYP1A expression,
which disappeared in cleared fish and whose F1 refractory response
overlapped with clean site F1 offspring. Decreasing GST activity was
evident in both clean and contaminated fish over time, with clean site
fish responding to contaminated sediment more deliberately. By 96 hours,
the response patterns of F1 offspring from clean and contaminated sites to
clean and contaminated sediment exposures were similar.   Because
p53, CYP1A and GST activity responses to contaminated sediment dosing
overlapped in clean and contaminated farm-raised F1 offspring, these
results suggest that contaminated fish have acclimated to the contaminants
present in their environments by reaching a tolerance threshold and no
evidence of adaptation was detected in these biomarkers.