Mercury concentrations in single event precipitation in southern Québec

Abstract

The paper presents one year of results (1995–1996) of an on-going research study in southern Québec with regard to mercury in precipitation. A modified rain water collector (MIC-B1) coupled to a data logger is used, in order to be able to select individual events from a remote site. A peristaltic pump coupled with an enclosed Teflon system train separates `in situ' the particulate and the dissolved phases of mercury. QA/QC sampling protocol including memory effect, percentage of recovery as well as field blanks are applied to maintain the high standards of quality. Total mercury concentrations in both phases are measured by Cold Vapour Atomic Fluorescence Spectrophotometry (CVAFS). The volume-weighted mean of total Hg concentration is 6.98 ng.l −1 (the median concentration is 6.58 ng.l −1 and the arithmetic mean is 8.26 ng.l −1). The annual total mercury deposition is about 7.6 μg.m −2. The particulate fraction accounts for a median of 26% of the total mercury concentration. According to Henry's Law, the truly dissolved mercury accounts for less than 0.5% whereas most of the dissolved fraction is expected to be in molecular complexes or colloidal form (<0.45 μm). A decreasing Hg concentration trend is observed with precipitation amount for both dissolved and particulate phases. Variability in the concentration and deposition ranges suggests complex chemical and scavenging processes.