Toxicity of copper in an oxic stream sediment receiving aquaculture effluent

Sediments were collected from a stream (upstream, outfall and downstream) r eceiving copper laden catfish pond effluent to assess toxicity to non-targe t biota. No significant reduction in Hyalella azteca survival or growth (10 d), or Typha latifolia germination and root and shoot growth (7 d) were ob served after exposure to upstream and outfall sediments. A significant redu ction in H. azteca survival was observed after exposure to the downstream s ediment sample; however, no reduction in T. latifolia germination or seedli ng growth was detected. Bulk sediment copper concentrations in the upstream , outfall and downstream samples were 29, 31, and 25 mg Cu/kg dry weight, r espectively. Interstitial water (IW) concentrations ranged from 0.053 to 0. 14 mg Cu/l with 10 d IW toxicity units greater than or equal to 0.7. Outfal l samples were amended with additional concentrations of copper sulfate so that bulk sediment measured concentrations in the amended samples were 172, 663, 1245, and 1515 mg Cu/kg dry weight. Survival was the most sensitive e ndpoint examined with respect to H. azteca with a no observed effects conce ntration (NOEC) and lowest observed effects concentration (LOEC) of 1245 an d 1515 mg Cu/kg, respectively. NOEC and LOEC for T. latifolia root growth w ere 663 and 1245 mg Cu/kg, respectively. IW copper concentrations were grea ter than or equal to 0.86 mg Cull with H. azteca intersitial water toxicity unit (IWTU) concentrations greater than or equal to 1.2, Sequential extrac tion qualitatively revealed the carbonate and iron oxide fractions which ac counted for a majority of the copper binding. In this instance, the copper which was applied to catfish ponds does not appear to be adversely impactin g the receiving stream system. (C) 2001 Elsevier Science Ltd. All rights re served.