Pesticide concentrations in sediment from irrigation areas can provide information required to assess exposure and fate of these chemicals in freshwater ecosystems and their likely impacts to the marine environment. In a study (Jochen et al., 2000), 103 sediment samples were collected from irrigation channels and drains in 11 agricultural areas of Queensland. In 74 of these samples, they detected DDTs with concentration levels up to 840 ngg–1 dw. Obtain a 95% confidence interval for the proportion of total number of sediments with detectable DDTs.