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Technical Memoranda 24
leGras CAA and Noller BN
Supervising Scientist, 1989
ISSN 0810-9532
ISBN 0 644 08623 8
Water from Magela Creek was sampled on 19 occasions at a location approximately 150 in downstream from the outflow of Georgetown Billabong during March-April 1986. Water was also sampled from two sites at Bowerbird Billabong, about 20 km upstream from Georgetown billabong. Samples were analysed for the total of all labile forms of zinc, operationally defined here as that portion of the metal mobilised by acidification of unfiltered samples to 0.1% (1 mL/L) with nitric acid giving a final pH of 1- 2. This is regarded generally as the fraction of zinc most available to biota. A rigorous sampling and analytical procedure to minimise contamination by extraneous zinc is described. The concentration of zinc in Magela Creek water varied from 87- 121 µg/L at Bowerbird Billabong and 196 - 738 µg/L at the site below Georgetown. At this site there was a positive correlation between zinc concentration and turbidity except during the flood event which occurred during the sampling period.
These data are compared with the statistically derived interim receiving water standard for zinc, and with acute lethal toxicity data on zinc for some Magela Creek fish species.