EXECUTIVE SUMMARY

Introduction

The Aquatic Effects Technology Evaluation Program AETE has been established to assist the Canadian mining industry in meeting its environmental effects monitoring and related requirements, in as cost-effective a manner as possible. The program is coordinated by the Canadian Center for Mineral and Energy Technology (CANMET). The present report is a technical evaluation of molluscs as biomonitoring tools for the mining industry.  Molluscs are a diverse taxonomic group that include bivalves and gastropods and are found widely distributed throughout Canada. Molluscs have been widely studied in both the laboratory and the field in order to evaluate their ability to serve as biomonitors of metals in the aquatic environment.

Evaluation

The present evaluation of molluscs as biomonitors is based on published studies conducted in the laboratory and field on mining contaminants of concern listed in the AQUAMIN Report (1996). Published field studies and reports of studies carried out by individual mining companies and the AETE program were consulted. Criteria for a good biomonitor and the work requirements of the contract were used as guidelines for the evaluation process. The following are the conclusions of this evaluation based on individual criteria.

1. Biomonitors should be relatively non-mobile in order that their exposure be representative of the study area. Molluscs are relatively sedentary although some species (i.e. unionids) may migrate short distances (meters) within their habitat. Bivalve molluscs are amenable to transplanting and caging. The sedentary nature and ease of caging of molluscs are advantages for site-specific monitoring not possessed by most fish.
2. Biomonitors should be abundant, widely distributed, easy to identify and sample at all times of the year. Molluscs are widely distributed across Canada and can be identified with limited taxonomic expertise. Limited information on the conservation status of molluscs suggests that most unionid bivalve species are currently stable in Canada.
3. Biomonitors should be large enough in body size to provide sufficient tissue for analysis. Individual unionid bivalves are large enough to provide sufficient tissue for metal analyses. Pooling of individuals of the smaller sphaeriids and most gastropods would be required for tissue metal analysis.
4. Biomonitors should be hardy, tolerating wide ranges of contaminant concentration and physiochemical variables. Molluscs are relatively hardy and tolerate wide ranges of metal concentrations, but are limited by pH below 4.7-5.0 and [Ca] below 2-2.5 mg/L.
5. Biomonitors should be strong accumulators of metals, with a simple correlation between metal concentrations in mollusc tissue and average ambient metal concentrations. Molluscs strongly accumulate metals (Cd, Cu, Zn, Pb, Ni, Hg, As, Ag and Cr). Field studies suggest that the relationship between mollusc tissue metal concentrations and ambient metal concentrations is influenced by a number of biological, physical and chemical parameters that need to be taken into account. Ultimately, the relationship is metal specific and depends on the availability of the metal from the dissolved and particulate phase.

Recommendations

1. Molluscs can be used as indicators of exposure to metals such as Cd, Cu, Zn, Pb, Ni, Hg, As, Cr, and Ag. Metal concentrations in bivalve molluscs could be used to:

• confirm changes in biologically-relevant metal concentrations in the natural environment resulting from mining activities.
• monitor long-term spatial and temporal trends in biologically-relevant metal concentrations by increases and decreases in tissue concentrations of indigenous or transplanted populations.
• determine the effectiveness of remedial measures through the use of transplanted and indigenous molluscs.

2. Molluscs are not stand alone tools. Numerous abiotic and biotic measurements must be made in conjunction with metal concentrations in molluscs to interpret effectively the results of field studies.
3.  Metal-induced effects in molluscs such as changes in growth or MT concentrations are not well established. These responses could be measured as part of the monitoring program, but their results should be used with caution as measures of effect until their role has been validated in field studies using mining contaminants.
4. Molluscs could be used in the first steps of a monitoring program in order to assess the extent of contamination in the aquatic environment. In more detailed information stages, molluscs may be used to investigate specific sources of bioavailable metals, improvements to waste-water treatment and effectiveness of remedial actions.
5. For comprehensive biomonitoring, molluscs can be used in conjunction with several other organisms (e.g. invertebrates, fish, plants) to monitor metals and their effects in the aquatic environment. In this way, information on the “biological consequences” of mining operations can be obtained, that is not available from monitoring sediment and water only.