Environmental Assessment
Volume E-5.4
Tailings Facility
Human and Ecological Health
Ambatovy Project
223
January 2006
Results
Water Quality
Aluminum, copper and iron were considered chemicals of potential concern in
the baseline risk assessment (Section 5.4.3) but they were not assessed further
since predicted concentrations are similar to baseline conditions and no
incremental risk for aquatic life is expected.
Water quality parameters which are expected to change due the operation of the
facility (Table 5.4-1) were screened against South African Guidelines for Aquatic
Ecosystems (1996). Alternative references were used for sulphate which is not
listed in the South African document (Recommended Guideline for Freshwater
Aquatic Life by Province of British Columbia, 2001). The data screening
indicated that sulphate and manganese did not warrant further consideration.
No guidelines for aquatic life are available for silicon. This element is
considered non-toxic and, based on recent literature, no negative environmental
effects related to this chemical have been reported. Therefore this potential
increase in surface waters in the study area is not considered environmentally
significant or warranting further risk analysis.
Zinc and magnesium were retained for further analysis and because
concentrations of zinc were above guidelines and because no guideline value is
available for magnesium.
Concentrations of zinc and magnesium were then divided by toxicity reference
values for algae, invertebrates and fish (Suter 1996) to calculate Hazard
Quotients (HQ) (see Volume K, Appendix 4.2 for description of risk estimation
of hazard quotients). The calculated HQs for each type of organism are
presented in Table 4.2-32 in Volume K, Appendix 4.2.
The HQ values for magnesium towards invertebrates and for zinc towards
invertebrates and fish were lower than 10 and considered negligible given the
conservative assumptions employed in water quality modelling as well as the
assumption of 100% bioavailability of these substances in the freely dissolved
phase.
The HQs for zinc towards algae were greater than 10 and could be of potential
concern. However, calculated HQ values for operation and post-closure phases
are similar to the HQ for the baseline conditions. Therefore incremental risk to
aquatic life due to tailings operations is unlikely to occur, and moreover, the
elevated background concentration would suggest local viable aquatic biota may
also have developed an increased metal tolerance which is a well-documented
physiological response.
