Environmental Toxicology of Perna Canaliculus

New Zealand does not have a major problem with marine pollution but there is still a need to develop methods to monitor the environment and protect ecosystems. Although some previous studies in New Zealand have measured the concentrations of chemicals in tissues from marine organisms, few to date have developed biomarkers of contaminant exposure. In the current study attempts were made to develop biomarkers for heavy metal contamination in the endemic New Zealand greenshell mussel Perna canaliculus. Metallothionein (MT) gene nucleotide sequences were isolated from P. canaliculus by cloning PCR products from genomic DNA. Nine MT exon 2 amino acid sequences were deduced, some of which were characterised by unusual features, including the presence of atypical tyrosine and histidine residues and lower than usual numbers of metal binding cysteine residues. MT sequences isolated in the current study were compared with those from other mollusc species worldwide. A 2-D gel DIGE proteomic approach was used to detect proteins involved in response to low salinity or heavy metal contamination. In the salinity study, control mussels were killed at the start of the experiment and others were exposed to ambient (32 ppt) and reduced (14 ppt) salinity for 3 days. Approximately 115 proteins showed significant (t-test p < 0.01) differences in abundance between the three experimental groups. Two isoforms of tropomyosin and one isoform of actin were identified and these proteins have been implicated in previous studies in response to reduced salinity. The low number of proteins identified in this study and the heavy metal experiment highlights the difficulty in working with invertebrate species that are presently underrepresented in the DNA and protein sequence databases. In the heavy metal experiment P. canaliculus were exposed to either 34.3 micrograms 1^1 Hg or 0.486 mg 1^1 Cd in the laboratory for 3 days. Control mussels were held in identical conditions without added metal. Over 100 proteins were detected which showed significant (p < 0.01) differences in abundance between control and metal treated groups but these proteins could not be identified using MALDI-TOF mass fingerprinting or tandem mass spectrometry. Tissue and time specific differences in metal uptake were observed. Proteins which responded to heavy metals under laboratory conditions were compared to field samples from the Bay of Islands. Approximately 30 proteins were detected which appeared to be associated with the presence of heavy metals under both field and laboratory conditions. These results suggest that it may be possible to develop biomarkers for heavy metal contamination in P. canaliculus. Based on the average concentrations of metals detected in the Bay of Islands, the amount of metal consumed through a typical diet containing shellfish would be below the provisional tolerable weekly intake (PTWI). However, because Maori, Pacific Islanders and Asians consume a greater quantity of seafood than the general New Zealand public a risk assessment for these groups was calculated. A survey of the frequency, amount and species consumed by these groups is suggested to enable an adequate risk assessment to be made.