Effect of endosulfan runoff from cotton fields on macroinvertebrates in the Namoi River

Of the several pesticides used in the pest management strategy for cotton, endosulfan is ranked as having the greatest impact on the riverine ecosyste m. A survey of changes in the densities of six abundant macroinvertebrate t axa (ephemeropteran nymphs Jappa kutera, Atalophlebia australis, Tasmanocoe nis sp., and Baetis sp. and two trichopteran larvae, Cheumatopsyche sp. and Ecnomus sp.) between upstream and downstream zones of the cotton-growing r egion in the Namoi River was conducted between November 1995 and February 1 996. In November and December 1995, there were few differences in populatio n densities between all sites. In January and February 1996, population den sities of the study taxa increased 7- to 10-fold higher at the two referenc e sites, with low concentrations of endosulfan in sediment and in passive s amplers placed in the water column. In contrast, densities of these taxa at sites with exposure to 25-foId higher concentrations of endosulfan remaine d static and were between one and two orders of magnitude lower than densit ies at the reference sites in January and February. Population densities of Baetis sp., a mobile ephemeropteran, did not indicate any inverse relation ship with endosulfan concentrations. Multivariate redundancy analysis indic ated that endosulfan concentrations were the leading environmental predicto r of changes in density of the five benethic taxa. Laboratory 48-h LC,, val ues of technical endosulfan in river water were 0.6, 1.3, and 0.4 ppb for e arly-instar nymphs of A. australis and J. kutera, and larvae of Cheumatopsy che sp., respectively. Endosulfan sulfate formed a large proportion of the total Endosulfan concentrations measured from in situ passive samplers, ind icating that its main route of entry into the river is through surface runo ff during Storm events. (C) 1999 Academic Press.