Are we analysing knockdown in the right way? How independence of the knockdown-recovery process from mortality may affect measures for behavioural effects in pesticide bioassays

In pesticide bioassays, especially those with neurotoxic agents, effects on animals are typically grouped into classes according to behaviour, such as normal and affected behaviour, which may range from unstable walking behav iour, to unable to move, to mortality. Generally, recovery is observed in a ll these effect classes, except the last. Mortality, however, disturbs the analysis of the recovery processes because it decreases the number of anima ls that otherwise could have shown a reversible effect. We consider that th is interaction between mortality and other, reversible, effects is a concep tual problem, and give arguments in favour of analysing changes in behaviou r and mortality as two independent, simultaneously occurring neurotoxic syn dromes. As an illustration, two data sets are analysed in both ways and the se show that marked differences may exist between conclusions reached by th e two viewpoints. The consequences thereof are discussed in relation to tox ico-kinetic explanations for neurotoxicant effects on behaviour and mortali ty. (C) 1999 Society of Chemical Industry .