Can the byssus of green-lipped mussel Perna viridis (Linnaeus) from the west coast of Peninsular Malaysia be a biomonitoring organ for Cd, Pb and Zn? Field and laboratory studies

Abstract

Concentrations of cadmium (Cd), lead (Pb) and zinc (Zn) in total soft tissues (ST) and byssus (BYS) of the green-lipped mussel Perna viridis from 11 different geographical locations off the west coast of Peninsular Malaysia were determined. The metal concentrations distributed between the BYS and ST were compared. The results of this study indicated that higher levels of Cd (1.31 μg/g), Pb (38.49 μg/g) and Zn (206.52 μg/g) were accumulated in the BYS than in the total ST (Cd: 0.29 μg/g; Pb: 8.27 μg/g; Zn: 102.6 μg/g). Semi-static and short period controlled laboratory experiments were also conducted for the accumulation and depuration of Cd, Pb and Zn in the total ST and BYS of P. viridis. The ratios (BYS/ST) for Pb and Cd from the laboratory experiments showed that the total ST accumulated more metals than the BYS. Therefore, these laboratory results disagreed with those found for the field samples. However, the laboratory results for the Zn ratio (BYS/ST) agreed with those of the field samples. It was evident that when compared to the ST, the BYS was a more sensitive biomonitoring organ for Zn while it could be a complementary organ for Cd and Pb in the total ST. Since total ST of P. viridis had been reported to have regulative mechanism for Zn, its BYS can be used as a biomonitoring organ for the identification of coastal areas exposed to Zn pollution.

Introduction

The ‘Mussel Watch’ approach focussed on the use of total soft tissues (ST) of mussels as a quantitative indicator to reflect the heavy metal contamination in the coastal areas Goldberg, 1975, Phillips, 1980, Phillips, 1985, Phillips, 1991, Phillips and Segar, 1986, Phillips and Rainbow, 1993. This common biomonitoring program involved the analysis of the total ST from the mussel after removing the byssus (BYS) and the shell. However, not all the metals are effectively accumulated in the ST of the mussels depending on the capability of the mussel species to accumulate and to regulate the metals. Green-lipped mussel Perna viridis regulates Zn in its ST (Phillips, 1985) and therefore making the use of total ST of this mussel species as an inefficient biomonitoring agent for Zn.

The use of total ST of P. viridis had been suggested as a potential biomonitoring agent of heavy metals for the west coast of Peninsular Malaysia (Ismail et al., 2000). Previous studies indicated that elevated levels of heavy metals were accumulated in the BYS compared to other ST of P. viridis (Ismail et al., 1999). This could be due to different tissues accumulating metals at different rates (Lakshmanan and Nambisan, 1989) with the different biological half-lives of the metals being related to the differing capacities of cells to eliminate the metals which are bound to the binding sites of the low molecular proteins (metallothioneins) Viarengo et al., 1980, Viarengo et al., 1985. Since heavy metals were readily accumulated in the BYS and the BYS showed high levels of metals (Ismail et al., 1999), the question of ‘whether the BYS can be used effectively as a complementary biomonitoring organ for heavy metals besides the total ST’ has been an interesting one.

The mussel BYS is selected for this ecotoxicological study because it has been shown to be of considerable importance in the storage and elimination of heavy metals in mussels Pentreath, 1973, Coombs and Keller, 1982, Koide et al., 1982, Ikuta, 1986a, Ikuta, 1986b, Cheung and Wong, 1992, Szefer et al., 1997a, Szefer et al., 1997b, Szefer et al., 1998, Szefer et al., 1999, Szefer et al., 2002. The use of the BYS of Mytilus species as a useful biomonitoring organ for heavy metals had been suggested by Koide et al. (1982). Heavy metal levels had been reported in the BYS of field collected Mytilus edulis from the Japanese coast Ikuta, 1986a, Ikuta, 1986b, Szefer et al., 1997a, Szefer et al., 1999 and P. perna from the Gulf of Aden, Yemen (Szefer et al., 1997b) and M. edulis trosulus from southern Baltic (Szefer et al., in press). These authors reported that the BYS of the Mytilus species could be a biomonitoring organ to assess the metal contamination besides the total ST. They even found that BYS could be a better biomonitoring organ for certain metals. Based on this information, we studied whether the BYS of P. viridis can be a biomonitoring organ for Cd, Pb and Zn.

There are several advantages of using the BYS of P. viridis as a biomonitoring organ for heavy metals. Firstly, the BYS can be easily pulled out from the foot after the death of the mussel. Secondly, it can also be handled in a similar way as human hair without a need for freezing (Sivalingam et al., 1983).

It must be emphasized here that there are no detailed reports on the heavy metals in the BYS of P. viridis from the west coast of Peninsular Malaysia except that reported by Sivalingam et al. (1983). In addition, there had been no published reports on metal concentrations in the BYS of marine mussels based on experimental conditions conducted in the laboratory.

In the present study, data from the field under natural conditions were collected. Laboratory studies were also conducted in order to test our hypothesis under controlled laboratory conditions (Chapman, 1995). In both natural and experimental samples, metal concentrations in both the BYS and ST were determined Ikuta, 1986a, Ikuta, 1986b, Szefer et al., 1997a, Szefer et al., 1997b, Szefer et al., 1999, Szefer et al., 2002.