Sediments collected near a wood-preserving plant on Thunder Bay Harbour, Canada, and highly contaminated by creosote (oil and grease content: 7600???80 000 mg/kg), PCP, metals, and other toxicants were found to be acutely toxic to mayflies (Hexagonia limbata) and leeches (Nephelopsis obscura) during a 10-day laboratory exposure study (Metcalfe & Hayton, 1989).