Mercury Contamination of the Lerderderg River, Victoria, Australia, from an Abandoned Gold Field
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Em~ironmentalPollution (Series A) 28 (1982) 135 147 This Project Report is publication No. 348 in the Ministry for Conservation of Victoria, Environmental Studies Series MERCURY CONTAMINATION OF THE LERDERDERG RIVER, VICTORIA, AUSTRALIA, FROM AN ABANDONED GOLD FIELD B. M. BYCROFT,*~ B. A. W. COLLER,* G. B. DEACON,* D, J. COLEMAN~ & P. S. LAKEs * Department of Chemistry. ~ Department of Zoology. Monash University, Clayton, Victoria 3168, Australia ABSTRACT In the catchment of the Lerderderg River, Victoria, Australia, gold-mining operations using the mercury amalgamation process were carried out until 50 years ago. The distribution of mercury in water, sediments and fish from the Lerderderg River has been investigated. Mercury in water values were low (0"01 to 0.31 I~g litre-1) and showed no clear correlation with sites of sampling. However, mereury concentrations up to 130 #g g-1 in sediments revealed a pattern of mercury contamination which could be related to past gold-mining activities. Elevated mercury levels were not found in brown trout Salmo trutta, but in river blackfish Gadopsis marmoratus, concentrations elevated to as much as 0"64 #g g- ~ were found in fish living at sites with elevated mercury sediment levels. INTRODUCTION Numerous studies in recent years have examined the contamination of biota by mercury from effluents. Attention has been largely devoted to discharges from chlor-alkali plants and papers-mills, quantitatively the most important on a world- wide basis (Newberne, 1974). Another potential source of significant local mercury contamination is that arising from the use of mercury in amalgamation processes for the extraction of gold and silver from ores. Although this extraction technique has been largely superseded by the cyanidation process, amalgamation was widely used in the early days on Victorian gold fields (Smyth, 1869). Significant levels of mercury are known to be contained in the tailings from amalgamation operations. For i" Present address: Marine Chemistry Laboratory, University of Melbourne, Parkville, Victoria 3052. Australia. 135 Environ. Pollut. Ser. A. 0143-1471/82/0028-0135/$02.75 © Applied Science Publishers Ltd, England, 1982 Printed in Great Britain 136 B.M. BYCROFTet al. example, tailings from an abandoned gold mine on the Thomson River, Victoria, Australia, contained 40--90#gg -1 of mercury (Melbourne and Metropolitan Board of Works, 1975). Similarly, tailings from a recently active mine near Woods Point, Victoria, Australia, have been found to contain 88 #g g- ~ of mercury (A. McCredie, pers. comm.). It has been estimated that the weight of mercury consumed in the amalgamation process is of the same order as the weight of gold recovered (Wise, 1966). On this basis, the potential mercury contamination from old gold- mining areas can reach major proportions. For instance, the amount of mercury potentially released to the environment from the Bendigo field, one of the richest early fields in Victoria, would amount to about 900 tonnes. Although it is many years since most Australian gold mines ceased operations, tailings dumps are still prominent features of the local landscape. Material from other dumps has been removed and possibly used for road surfacing or as filling materials in creeks and gullies. Thus, there is potential for a continuing release of mercury from these tailings into adjacent aquatic environments. There are some reports in the literature of studies of mercury contamination from amalgamation processes (e.g. Van Meter, 1972; Walter et al., 1973; Moore & Sutherland, 1980). In Victorian studies, mercury accumulation has been reported in the Woods Point area, near mines recently in operation (Environment Protection Authority, Victoria, 1982), and in the Gippsland Lakes, downstream from areas which, until the 1930s, were mined for gold (Glover et al., 1980). A preliminary study by the Victorian State Rivers and Water Supply Commission (Bennison & Guest, 1980) indicated that parts of the upper Lerderderg River have elevated levels of mercury. It appeared that this could possibly arise lrom adjacent abandoned gold fields at Blackwood. This paper reports on the distribution of mercury in water, sediments and fish from the Lerderderg River and the relationship between mercury levels and gold- mining activities around Blackwood. It forms part of a larger study, funded by the Environmental Studies Section, Victorian Ministry for Conservation, to investigate the sources and distribution of selected heavy metals in the Lerderderg-Upper Werribee Rivers catchment. Alluvial gold was first discovered near Blackwood in 1851 (Buckingham & Hitchcock, 1980). By 1855 much of the alluvial gold had been recovered, and reef- mining operations began. From 1869, when detailed recording began, over 5000 kg were won from the Blackwood field (Buckingham & Hitchcock, 1980). The largest mine, the Sultan, ceased operations in 1883. However, one mine, the Trojan, from which about 140 kg of gold was recovered (Foster, 1937), operated until about 1937 (L. Armstrong, pers. comm.). Although amalgamation was originally used to recover the gold, later operations in the 1930s involved reworking, by cyanidation, of tailings from amalgamation processes in order to recover residual gold. It is probably more than 50 years since direct amalgamation was used routinely on the Blackwood field. MERCURY IN AN AUSTRALIAN RIVER 137 DESCRIPTION OF THE STUDY AREA (FIG. 1) The Lerderderg River rises on the southern edge of the Great Dividing Range, about 110 km northwest of Melbourne. State forest covers most of the catchment. The river, 60km long, flows approximately in a southeasterly direction, passing through the settlements of Blackwood and Darley before joining the Werribee River. The mean discharge is relatively low, 27.3 megalitres a year (Australian Water Resources Council, 1979). The flow regime is quite variable with generally a spring peak and a summer low (often zero) matching the seasonal pattern of rainfall in the catchment. When the river is flowing, the conductivity in the upper reaches is generally about 100-120/~S cm- 1. The conductivity rises to about 300/~S cm - 1 as the river passes through the agricultural land around Darley. The pH of the water is generally slightly alkaline. Under normal conditions the transparency of the water and the dissolved oxygen are both high--an indication of little organic pollution. Recently, a weir and diversion tunnel were constructed on the river (see Fig. 1). The purpose of these constructions is to divert water from the upper Lerderderg River to Merrimu Reservoir which supplies drinking and irrigation water to surrounding districts. MATERIALS AND METHODS Sample collection Water, sediment and fish samples were collected from sites along the Lerderderg River and its tributaries, with sampling points focused around Blackwood (see Fig. 1 for location of sampling sites). Samples were also collected from a control site on the adjacent Werribee River, upstream of its confluence with the Lerderderg River. Relatively little gold mining took place in the upper Werribee River catchment. The (surface) water samples were collected weekly over a period of six weeks in October November 1979 when the river level was dropping. A 250 ml aliquot was filtered under pressure through pre-washed membrane filters (0.45/~m, Millipore 47 mm, HAWP) in a plastic (Sartorius) filtration apparatus. The filtered sample was transferred to a BOD bottle (Wheaton) containing 2.5 ml of concentrated nitric acid (BDH, Aristar Grade) and 5 ml of 4 % potassium dichromate (Ajax, Analar Grade) as preservative. The membrane filters were transferred to labelled plastic petri dishes. Field blanks were prepared by the filtration of 250 ml aliquots of distilled water. On each sampling trip the blank was prepared at a different site. All filtered water samples were stored at 4°C and analysed the day following collection. The sediment samples were collected in a summer period, January 1980, and a winter period, August 1980. They were wet-sieved in the field using river water. The complete fraction which passed through a 180/~m (80 mesh) nylon sieve was retained to avoid loss of fines which settled very slowly and may have contained a ! ! • I o q ~ ~ H ! ~z t i ii &,, . I -._-" 0~|• r I .--, "-;. ~4 "--., "?t ~ Ir J¢ i" i ( ,,J t ~ i .-- -._;I 70 2a ±~oaaxtt '~ 'a g~ I MERCURY IN AN AUSTRALIAN RIVER 139 substantial proportion of the mercury. Up to three separate samples were collected at each site. An aliquot of the resulting sediment slurry was transferred to a glass- stoppered glass jar, and was used for mercury analysis. A separate aliquot of the well mixed slurry was transferred to a screw-cap jar. This sample was used for percentage moisture determination to allow calculation of the mercury levels on a dry weight basis. Fish were sampled by electroshocking using a custom-built electrofishing unit (240 V pulsed DC) powered by a Honda 1000 W generator. The fish were placed in plastic bags. All sediments and fish were placed on ice for transport to the laboratory where they were stored at -10°C until analysis. Analytical procedures The filtered water sample was analysed for mercury by the method of the Victorian Environment Protection Authority (H. Blutstein, pers. comm.). Briefly, a 100 ml aliquot of the preserved water sample was digested on a boiling water bath with 0.5g potassium permanganate (Merck No. 5084, low mercury) and 0.3g potassium persulphate (Ajax, Univar). The precipitated manganese dioxide and excess permanganate were reduced by ascorbic acid. The membrane filter contain- ing the non-filtrable residue was analysed for mercury by the aqua-regia/- permanganate method of the US Environmental Protection Agency (1974) for mercury in sediments. The aqua-regia (one part nitric acid to three parts hydrochloric acid) was prepared from Aristar (BDH) grade reagents. An aliquot of the sediment slurry was digested prior to mercury analysis using the procedure of the US Environmental Protection Agency (1974). Each sample was analysed in triplicate.