METAL CONCENTRATIONS IN MYTILUS EDULIS AND MYA ARENARIA LIVING IN AND AROUND TAILINGS FROM AN ABANDONED COPPER MINE

Geoff Veinott* and Robin Anderson, Habitat and Toxicology Research Section, Northwest Atlantic Fisheries Centre, Department of Fisheries and Oceans, St. John’s, NF. CANADA. A1C 5X1. Telephone 709-772-7989. Fax. 709-772-5315. Email veinottg@athena.nwafc.nf.ca

Paul Sylvester and Dewan Gani, Department of Earth Sciences, Memorial University of Newfoundland, St. John’s, NF. CANADA

*Author to who all correspondence should be directed.

ABSTRACT

Concentrations of V, Mn, Fe, Co, Ni, and Cu were significantly higher in the soft tissue of Mytilus edulis and Mya arenaria living in and around tailings from an abandoned Cu mine (Little Bay) compared to samples from the reference site (Smith’s Harbour). Despite the elevated metal levels in the soft tissue both species are plentiful at the study site and appear healthy. Both species appear to be able to regulate Cu body burdens which may explain their ability to tolerate this environment. Nevertheless, the Cu concentrations in Mytilus edulis reported here are some of the highest levels found in wild populations of Mytilus edulis in the world. Our mean Cu concentration of 45 mg .g^-1 dry weight is double the World Mussel Watch 85^th percentile value of 21 mg .g^-1 dry weight for Mytilus edulis

INTRODUCTION

In Canada submarine tailings disposal (STD) is no longer seen as an acceptable method for the disposal of mine waste. However, the alternatives (disposal to a lake, pit, or dammed impoundment) may not be less damaging to the environment. As well, surface disposal in a dam impoundment requires maintenance of the dam in perpetuity.

Little Bay in Notre Dame Bay in Newfoundland, Canada is the site of an abandoned copper mine. Tailings from the mine were deposited behind a dam in Shoal Arm, a narrow bay off Little Bay Arm. The mine closed in 1969 and the tailings impoundment dam breached in 1974 releasing tailings to the marine environment. Spring melt and storm events continue to flush tailings from the dry impoundment into the marine environment.

Blue mussel (Mytilus edulis) live attached to rocks on the edge of the tailings delta and the tailings delta has become inhabited by soft shelled clams (Mya arenaria). Both of the shellfish species are harvested by the local population for personal consumption.

This study is part of a larger project examining the chemical and ecotoxicological impact of STD. The purpose of this study was to compare the levels of V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb in mollusks at the mine site to a “clean” site. The data will be used as a baseline for future studies to delimit the impact zone of the tailings, for monitoring changes in the metal levels, and to evaluate risk due to consumption of mollusks from the area.

METHODS

Mussels and clams were collected by hand in the tidal zone. Specimens were depurated in seawater for 48 hours, placed on ice at 4^OC and returned to the laboratory where they were placed whole in freezers at -14^OC. Prior to analyses specimens were thawed, shucked, and rinsed in distilled water. M. arenaria had the sheath covering their siphons removed as well as their guts whereas the entire body of M. edulis was retained for analyses. Next, the soft tissue of 5 individuals were combined, and dried at 100^OC for a minimum of 12 hours. After drying, specimens were roasted in a muffle furnace at 500^OC for 12 hours and then digested in concentrated nitric acid. Aliquots of the digested material were diluted and analyzed for their metal content by ICP-MS. Differences in the soft tissue mean metal concentrations due to species and site were tested for using a two way Anova.

RESULTS AND DISCUSSION

Results from the analyses of the mollusk tissue are given in Table 1. There was a significant difference (p<0.05) in the concentrations of V, Mn, Fe, Co, Ni, Cu, and Pb, between the study site (Little Bay) and the reference or clean site (Smith’s Harbour). This is not surprising as many studies have shown that both these species will accumulate metals from their environment (see for example Pempkowiak et al 1999, Gibb et al. 1996). There were also significant differences in the metal concentration between species (V, Cr, Fe, Co, Ni, Zn, Cd, Pb) with M. edulis having the higher concentration in each case. This may have been due in part to the removal of the guts from M. arenaria. Szefer et al. (1990) reported that approximately 20% of the Cu, Zn, and Cd in M. arenaria was found in the digestive system. However, there was clearly sediment present in the guts of our specimens as well as on the siphon sheath. It was felt that removing the contamination would provide a better indication of the true metal concentration in the tissue. In spite of this potential loss of material from the analyses, the large and significant changes in Mn, Co, and Cu between sites in both species strongly suggest that the environment is the major cause of the observed differences in tissue concentration.

Little Bay is a unique site in that it is some what isolated with no heavy industry or large urban centres in the region. Therefore, the tailings are the only source of heavy metals to the area. Copper is of particular interest because we are dealing with an abandoned copper mine. As well, copper is an essential element and can be regulated by M. edulis (Han et al. 1993, Phillips 1976). However the concentrations of Cu reported here are some of the highest levels found in wild populations of M. edulus in the world. Our mean Cu concentration of 45 mg .g^-1 dry weight is double the World Mussel Watch 85^th percentile value of 21 mg .g^-1 dry weight (Cantillo 1998). This suggests that there is an upper limit on the concentration of Cu that can be accumulated by M. edulis and that the Little Bay mussels are near that upper limit.

There was no significant difference in the Cu concentrations of M. arenaria and M. edulis. However, M. arenaria can accumulate many hundreds of mg of Cu per g of dry weight when exposed to high concentrations of the cupric ion in water (Wright and Zamuda 1987). A tolerance for environments with elevated levels of Cu may explain M. arenaria’s ability to colonize and survive on the tailings delta. As well as survive being repeatedly exposed to fresh tailings from the dry tailings dump.

Despite living in and around the tailings from a copper mine both mollusk populations appear healthy and plentiful. Their apparent ability to regulate the amount of Cu retained in their soft tissue gives them a distinct advantage in this environment. However, M. edulis appears to be near its upper limit of accumulation. It is unclear what effect a sudden influx of fresh tailings (e.g. a large storm event) would have on the health of these animals.

Table 1 Metal concentrations in the soft tissue of Mytilus edulis and Mya arenaria. Concentrations are reported as mg . g^-1 dry weight.
		Little Bay		Smith’s Hr.
Element	Species	Mean	Std Dev.	Mean	Std Dev.
V	Mytilus	4.38	0.43	1.01	0.08
	Mya	0.68	0.10	0.20	0.03
Cr	Mytilus	2.26	0.30	2.10	0.45
	Mya	0.35	0.10	0.06	0.01
Mn	Mytilus	18.9	1.4	4.4	0.4
	Mya	18.2	5.5	1.4	0.2
Fe	Mytilus	1483	217	409	72
	Mya	254	85	87	7
Co	Mytilus	4.25	1.05	0.79	0.14
	Mya	3.01	0.18	0.17	0.04
Ni	Mytilus	2.18	0.64	2.01	0.19
	Mya	2.51	0.44	0.40	0.06
Cu	Mytilus	44.8	4.2	7.4	0.3
	Mya	62.5	19.0	7.0	1.3
Zn	Mytilus	77	16	89	13
	Mya	74	14	59	5
Cd	Mytilus	1.89	0.05	2.23	0.52
	Mya	1.03	0.12	0.58	0.12
Pb	Mytilus	0.49	0.07	3.69	0.64
	Mya	0.03	0.01	0.18	0.04

REFERENCES

Cantillo, AY (1998), Mar. Poll. 36:712-717.

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Han, BC, Jeng, WL, Tsai, YN, Jeng, MS (1993), Environ. Poll. 82:93-97

Pempkowiak, J, Sikora, A, Biernacka, E (1999), Chemosphere 39:313-321.

Philips, DJH (1976), Mar. Biol. 38:59-69

Szefer,P, Szefer, K, Skwarzec B (1990), Mar. Poll. Bull. 21:60-62.

Wright, DA, Zamuda, CD (1987), Mar. Environ. Res.23:1-14.