الفهرس 
Routes of exposure and target organs for metals in bivalvesOnly 14 pages are availabe for public view
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Abstract
The immunotoxic effects of trace metal exposure in bivalves are poorly understood
and whether or not stimulation of the immune system exacerbates metal toxicity is still
unclear. The mussel, Mytilus edulis, was exposed to 50 or 500 μg l-1 total Hg or 20 or 50 μg l-
1 total Cd for up to 11 days compared to no added Hg or Cd controls. Selected experiments
were then repeated in mussels injected with lipopolysaccharide (LPS) to challenge the
immune system with or without exposure to 50 μg l-1 Hg or 20 μg l-1 Cd for 8 days. Immune
functions of haemocytes, haematology, haemolymph glucose, electrolytes, superoxide
dismutase (SOD) activity and organ pathology were measured. Hg accumulated mainly in
gills and Cd in digestive gland. Hg or Cd exposure alone caused transient modulation of
haemocyte immune functions, and haemolymph Na, K and glucose levels were negligible.
LPS injection had a significant effect on haemocyte numbers and variable response patterns
in phagocytosis and neutral red uptake (NRU) compared to other mussel groups. Tissue
pathology was shown in Hg and Cd exposures and greatly increased by the effect of LPS
injection. In conclusion immunostimulation with LPS can increase Hg or Cd-related organ
pathologies, but not necessarily alter the responses of haemocytes. Mussels collected from
field are widley used to assess the effects of pollution on the aquatic environment, and the
effect of pre-exposure history on the immunological response to subsequent metal exposure is
poorly understood. The current work aimed to compare the health status in animals from a
clean to a contaminated site in South West England to determine whether these end points
could be useful in biomonitoring. Mytilus edulis were collected from both sites and analysed
for trace metals, cellular immune responses, biochemistry, and condition index (CI) and
III
histopathology. Groups of mussels from each site were exposed to 20 μg l-1 CdCl2 for up to 8
days compared to unexposed controls. End points were tissue and hamolymph
metals/electrolytes, cellular immune functions and histology. For field work, concentrations
of Cd, Cu, Fe, Zn and Pb were significantly higher in mussels from the polluted site. A strong
correlation between shell length and metal concentration was observed. Pollution had an
effect on NRR, (CI), and tissue pathology of polluted site mussels. For the laboratory study,
immune functions, CI and Na or K levels did not follow clear trends in site or Cd exposure
effects. Tissue necrosis and inflammation in animals from the polluted sites were shown, but
Cd exposure improved some of these pathologies. I conclude that metal pollution modulates
biological functions in M. edulis, but pre-exposure history has limited effects on these
responses. Tissue histology is a sensitive tool to distinguish clean from polluted sites.