Analysis and Temporal Variations of Trace Metals in Precipitation at an Atlantic Station

Abstract

Weekly and half-monthly bulk samples have been collected over one year at an Atlantic station and routinely analysed for 0.08 M HNO₃-leachable trace metals Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn by direct electrothermal atomic absorption spectrometry. In the presence of sea salt, interference effects may lead to important erroneous metal concentrations if peak height measurements and direct calibration with aqueous standards are used. Interference effects are minimized (to about 5%) by using integrated absorbance measurements for sea salt solutions having C_Na< 100 mg/l and using standards prepared in the presence of sea salt (20 mg/l in Na). The variability of trace-metal determinations obtained for six bulk collectors for each sampling event shows that our entire analytical protocol, sampling and analysis, permits to follow their temporal variations at a coastal station for weekly or half-monthly sampling periods. A high correlation is obtained for anthropogenic metals Cd, Cu, Ni, Pb and Zn. For Cr, Fe and Mn, significant correlations with anthropogenic metals indicate both anthropogenic and crustal sources. No correlation with Na is observed. At this Atlantic station, trace-metal concentrations and annual deposition densities are significantly lower than at European stations around the North Sea which are more subject to industrial emissions.

Key Words:

• Precipitation
• Atlantic
• trace metals
• sampling
• analysis
• variability
• metal correlations