Pollution by arsenic in a gold-mining district in Nova Scotia

Abstract

Arsenic levels were determined in arseniferous gold tailings, waters, stream sediments, plants and aquatic organisms in the vicinity of a stream draining the Montague gold mining district near Halifax, Nova Scotia. Background levels of arsenic in Mitchell Brook, upstream from the former mining activities, were high (37 ng ml −1), although below the safety limit of 50 ng ml −1. Levels did, however, decrease, due perhaps to ion exchange during passage of the water through a non-polluted swamp, but then increased to 190 ng ml −1 as the stream passed through the arseniferous gold trailings of the abandoned Montague Gold Mine. Thereafter, levels decreased again and reached 46 ng ml −1 at the outflow in Lake Charles. Arsenic levels in tailings were inordinately high and ranged from 0·38% to 0·65%, being highest in the downslope areas. In stream sediments (clay and quartz fractions), arsenic levels increased considerably in the vicinity of the mine and remained high for most of the remaining course of the stream. Arsenic levels in ashed twigs of alder Alnus rugosa growing on the stream banks correlated well with arsenic levels in water except where the latter became excessively high. The arsenic content of aquatic organisms correlated well with the arsenic content of water and ranged from 0·002 to 0·059 μg g −1 (dry weight) for mayfly larvae, 0·002 to 0·18 μg −1 (dry weight) for caddisfly larvae and 0·63 to 3·2 μg g −1 (wet weight) for the banded killifish (minnow). It is concluded that arsenic pollution from former gold mining activities in this area is appreciable and it is suggested than in future gold mining operations care should be taken to isolate arseniferous tailings from local drainage systems.