Flux of heavy metal accumulation in various organs of the intertidal marine blue crab, Portunus pelagicus (L.) from the Kuwait coast after the Gulf War
Introduction
Trace elements are found in natural water bodies at varying concentrations. The most potentially dangerous of these elements are heavy metals, viz., Pb, Cd, and Hg, and the metalloids, viz., As, Se, and Sb. Heavy metals have a great affinity for sulfur and attack sulfur bonds in enzymes of marine organisms thus immobilizing the latter. Other vulnerable sites are protein carboxylic acid (–CO2H) and amino (–NH2) groups. They also tend to precipitate phosphate bicompounds or catalyze their decomposition. Body levels of essential metals such as copper and zinc can be regulated by some crustacea at concentrations below a threshold level. Accumulation of these metals only begins after the organisms are faced with high concentration in the surrounding medium Rainbow, 1985, Rainbow and White, 1989. In contrast, body levels of nonessential metals such as mercury, cadmium, and lead were not found to be regulated by crustacea Krishnaja et al., 1987, Pastor et al., 1988.
In Kuwait, trace metal input may be derived from a number of anthropogenic and natural sources. Metal such as, arsenic, selenium, and mercury have been found to enter coastal waters by sewage and other wastewater effluents, power plant cooling water discharges, auto emissions, petroleum and petrochemical industrial wastes, storm drain outfalls, and solid waste landfills (UNEP, 1980). In addition to these anthropogenic sources, trace metals have also been found to be introduced into local marine waters adsorbed on airborne and waterborne particulate material (Anderlini et al., 1982).
This study has been undertaken to determine (a) the concentration levels of arsenic, chromium, copper, lead, magnesium, manganese, selenium, vanadium, and zinc in various body organs, viz., hepatopancreas, gills, gonad, gastric stomach, and muscle of the blue crab, Portunus pelagicus L., (b) to investigate the correlation coefficient between each metal, (c) to examine the correlation between metal concentration and the different crab organs tissue, and (d) significant difference in metal concentration (if any) between male and female crabs.
Section snippets
Locations
A total of 45 crab samples were collected from three different locations of the Kuwait Bay to provide a representative coverage of the Kuwait Bay (Fig. 1). The crabs were caught by a traditional fishing method “Hadhra” erected at the intertidal zones along the shores of Kuwait City between May 1998–April 1999. Such shores had been affected by oil spills during the Iraqi invasion of Kuwait.
Method
Out of the 45 crab samples of P. pelagicus examined, there were 22 males and 23 females. A total of 15 crab
Results and discussion
The trace metal data on the P. pelagicus organs/tissues from the three stations are presented in Table 2. Comparison of mean concentrations of trace metals reported in decapod crustaceans for other world areas are given in Table 3. All the data were found to be above detection limits. Logarithmic values were used to derive a linear regression model and condense the data to express linearity. Factors influencing the concentration of trace metals in marine organisms include species differences
Conclusion
In conclusion, the differences in the pattern of metal occurrence in various organs of the crab, P. pelagicus, and the significant increase of Cu and Zn concentrations are likely associated with the contribution from the 1991 Gulf War oil spill into Kuwait's marine environment. This clearly indicates the ability of decapods to accumulate metals to detectable levels. Metal bioaccumulation by crabs can be affected by the chemical composition of the sediment and interstitial seawater (Sadiq, 1992)
Acknowledgements
We extend our thanks to the personnel of the Science Analytical Facilities (SAF), Kuwait University, for their assistance on the heavy metal analyses.
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