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Purpose: Risk assessment of contaminated sediments is routinely based on laboratory exposures. The purpose of this work was to study if sediments contaminated by the chemical wood industry cause developmental defects in fish fry and how well a laboratory exposure correlates with a field exposure. Materials and methods: Newly hatched yolk-sac fry of rainbow trout ( Oncorhynchus mykiss) were exposed in the laboratory and in situ. In the laboratory, the fish were placed in contact with either clean or contaminated sediment in aquaria. In the field, half of the fish were placed in contact with the lake sediment and the other half were similarly caged 2 m above it, to discern the effects of the sediment from that of the effluent. When approximately three fourths of the yolk was consumed, the fry were examined for blue sac disease (BSD) symptoms, their length and yolk volume were determined, and cyp1a and cyp1c2 transcript abundances were measured with quantitative PCR. Results and discussion: The sediments did not cause mortality, developmental defects, or upregulation of cyp1a or cyp1c2 in the laboratory. No severe BSD was detected in the field exposure, but mortality was higher in embryos caged on the sediment than in those kept 2 m above the bottom and in those exposed in the laboratory. Unlike the laboratory exposure, the field exposure to contaminated sediments reduced the growth of the fry. Conclusions: Laboratory exposures may underestimate the risk that contaminated sediments pose to developing fish. This should be taken into account in risk assessment. [ABSTRACT FROM AUTHOR]