DIFFERENT FACTORS RELATED TO MERCURY CONCENTRATION IN SEDIMENTS AND ZOOPLANKTON OF 73 CANADIAN LAKES A. TREMBLAY l, M. LUCOTI'E 1 and D. ROWAN 2 1 Chaire de recherche en environnement Hydro-Qu~bec/CRSNG]UQAM, Universit~ du Qutbec ~tMontreal, C. P. 8888, Succ. Centre vine, Montreal, Quebec, tt3C 3P8, Canada. 2 EnvironmentalResearch Branch, Chalk River Laboratories, Chalk River, Ontario, K0J 1J0, Canada. Abstract: Sufficial sediments were sampled with a light-weight gravity corer at 175 sites in 73 Ontario and Qntbec lakes and zooplankton was collected with a 225 pm mesh size net in 24 lakes. Hg concentrations in surficial sediments (0-2 cm) ranged from 3 to 267 ng g-1 dry weight with a mean of 80 ng g-1 dry weight for all sites. A regression model including organic content of sediments and the ratio of the catchment area / lake surface explained 60% of the variation in sediments Hg concentrations. Hg in zooplankton ranged from about 25 to 377 ng g-1 dw with a mean of 108 ng g-1 dw and was weakly correlated with catchment area, primary productivity and TOC. Our data indicate that an important fraction of Hg originates from the catchments, but do not show a clear west-east regional gradient for Hg concentrations in surficial sediments or in zooplankton. 1. Introduction During the past few decades, attention paid to mercury (Hg) pollution and its effects on human health, due to the consumption of contaminated food, has been extended from locally polluted areas to regions remote from anthropogenic sources of contamination. Canada, Scandinavia and theUnited States are particularly affected with Hg concentrations in fish of many natural and artificial aquatic environments often exceeding public health guidelines (0.5-1.0 mg kg -1) (Hfikanson et al., 1988; McMurtry et al., 1989; Meili, 1991a; Lathrop et al., 1991). The magnitude of the problem in remote lakes is illustrated by the fact that in Sweden, over 10 000 natural lakes are presently estimated to bear predatory fish having Hg concentrations greater than 1 mg kg -1 weight weight (ww) for a body weight of I kg. Furthermore, the "Sport Fishing Guide" of Ontario and the "Guide de consommation du poisson de p~che sportive en eau douce" of Qutbec propose limited consumption of certain species of fish for 30 to 40% of the studied lakes (all remote from industrial centres). Although opinions regarding the reasons for the widespread Hg contamination of lakes vary considerably, long distance atmospheric transport is suggested as the primary source of Hg to remote regions (Bjtrklund et al., 1984; Swain et al., 1992; Lucotte et al., 1994). Having an estimated residence time of one year (Lindqvist and Rodhe, 1985; Nater and Grigal, 1992), atmospheric Hg is deposited via wet and dry precipitation, and enters lakes either directly or from the catchment area and will Water, Air, and Soil Pollution 80: 961-970, 1995. 9 1995 Kluwer Academic Publishers. Printed in the Netherlands.