Chronic intoxication by an herbicide, 2,4,5-trichlorophenoxyacetic acid, in the pond snail, Lymnaea stagnalis L

Experiments of chronic intoxication with three concentrations (10, 20, and 40 ppm) of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) were conducted in the freshwater mollusc Lymnaea stagnalis. Snail survival was concentration dependent. In all cases the growth can be described by the von Bertalanffy pattern (ht = h (1 - e-k(t-to)) and the variations of the k values showed that growth was significantly altered in all the groups treated. The overall fecundity (F) was always reduced; the decrease was due both to a lower number of eggs per egg mass (-7.8 to -12%) and to an earlier death of the intoxicated snails. Fecundity studied in terms of size, according to the law F = ahz, points out the loss of equilibrium between growth and fecundity: in all groups treated the values of the exponent z were increased. The importance of these perturbations can be quantified by the calculation of a "Snail Yield" which is reduced by 72.6% in the 40 ppm group. Egg fertility was also reduced. It can be concluded that 2,4,5-T disturbs the physiological equilibrium of Lymnaea stagnalis leading even to earlier death of the snails.