Can the shell of the green-lipped mussel Perna viridis from the west coast of Peninsular Malaysia be a potential biomonitoring material for Cd, Pb and Zn?

Abstract

The distributions of Cd, Pb and Zn in the total soft tissues and total shells of the green-lipped mussel Perna viridis were studied in field collected samples as well as from laboratory experimental samples. The results showed that Cd, Pb and Zn were readily accumulated in the whole shells. In mussels sampled from 12 locations along the west coast of Peninsular Malaysia, the ratios of the shell metals to the soft tissue metals were different at each sampling site. Nevertheless, the Cd and Pb levels in the shells were always higher than those in the soft tissues, while the Zn level was higher in the soft tissues than in the shells. In comparison with soft tissues, the degrees of variability for Pb and Cd concentrations in the shells were lower. The lower degrees of variability and significant (P<0.05) correlation coefficients of Cd and Pb within the shells support the use of the mussel shell as a suitable biomonitoring material for the two metals rather than the soft tissue since this indicated that there is more precision (lower CV) in the determination of metal concentrations in the shell than in the soft tissue. Experimental work showed that the pattern of depuration in the shell was not similar to that of the soft tissue although their patterns of accumulation were similar. This indicated that the depuration of heavy metals in the shell was not affected by the physiological conditions of the mussels. Although Zn could be regulated by the soft tissue, the incorporated Cd, Pb and Zn remained in the shell matrices. The present results support the use of the total shell of P. viridis as a potential biomonitoring material for long-term contamination of Cd, Pb and Zn.

Introduction

‘Can the hard tissues of bivalves such as the shells be used as biomonitoring materials?’ has been an interesting question. The international ‘Mussel Watch’ programme focussed on the soft tissues of mussels rather than the mussel shells to monitor heavy metal contamination in coastal waters (Goldberg, 1975, Goldberg, 1980, Phillips, 1980, Phillips, 1985, Phillips, 1991, Phillips and Segar, 1986, Phillips and Rainbow, 1993, Ismail et al., 2000). The measurement of heavy metals in the soft tissues of mussels may, however, be unduly influenced by factors such as metal variability due to gonadal conditions (Lobel, Bajdik, Jackson, & Longerich, 1991), seasons of rainfall and heterogenous habitats rather than due to regular inputs of anthropogenic metals into the coastal waters. In addition, total soft tissues of mussels might not effectively accumulate certain metals. In the case of the green-lipped mussel Perna viridis, the presence of a regulatory mechanism for Zn levels in their soft tissues has been reported (Phillips, 1985).

The use of mussel shells for the biomonitoring of heavy metals is not a new idea since several studies have already been reported (Phillips, 1980, Goldberg, 1975, Goldberg, 1980, Goldberg et al., 1978, Koide, Lee and Goldberg, 1982, Phillips and Rainbow, 1993). This is due to marine mussels generally fulfilling the recommended criteria for a good biomonitor (Phillips, 1985, Phillips and Segar, 1986, Phillips, 1991, Phillips and Rainbow, 1993). Several authors have investigated the heavy metal concentrations of mussel shells (Sturesson, 1976, Sturesson, 1978, Imlay, 1982, Koide, Lee and Goldberg, 1982, Wilbur and Saleuddin, 1983, Al-Dabbas, Hubbard and McManus, 1984, Szefer and Szefer, 1985, Carell et al., 1987, Puente, Villares, Carral and Carballeira, 1996, Szefer et al., 2002) and the shells of other molluscs species (Szefer and Szefer, 1985, Dermott and Lum, 1986, Walsh, Dunstan and Murdoch, 1995, Foster & Chacko, 1995, De Wolf, Ulomi, Beckeljau, Pratap and Blust, 2001). Most of the studies concluded that molluscs' shells could be used as potential biomonitoring materials although some studies concluded otherwise.

A comparison of the metal levels in the shells and the total soft tissues of mussels to determine the potential use of molluscs' shells as a biomonitoring material for heavy metals has been used by several authors (Pilkey and Goodel, 1963, Segar, Collins and Riley, 1971, Bertine and Goldberg, 1972, Graham, 1972, Koide, Lee and Goldberg, 1982, Szefer and Szefer, 1985, Dermott and Lum, 1986, Newman, Mulvey, Beeby, Hurst and Richmond, 1994, Puente, Villares, Carral and Carballeira, 1996, Giusti, Williamson, & Mistry, 1999, Szefer et al., 2002). In the present study, the same comparison was used to determine whether the shells of P. viridis could be a biomonitoring material for Cd, Pb and Zn. In addition, its potential use as a biomonitoring material for these three metals was also studied based on the associations (correlations) of these metals, and their ability to accumulate these metals, the degrees of metal variability (coefficients of variation) and patterns of accumulation and depuration of the metals in the shells and the soft tissues of P. viridis. It should be emphasised here that there has been no published report on the use of the mussel shell as a biomonitoring material for heavy metals in Malaysia. The objective of this study is to determine the potential of the shell of P. viridis as a biomonitoring material for Cd, Pb and Zn based on field and laboratory experimental samples.