Statistical refinements for data analysis of mollusc reproduction tests: an example with Lymnaea stagnalis

Sandrine Charles

Publikation: Konferencebidrag uden forlag/tidsskriftKonferenceabstrakt til konferenceForskning


Since 2012, European experts work towards the development and
validation of an OECD test guideline for mollusc reproductive toxicity
with the freshwater gastropod Lymnaea stagnalis. A ring-test involving
six laboratories allowed studying reproducibility of results, based on
survival and reproduction data of snails monitored over 56 days
exposure to cadmium. A classical statistical analysis of data was initially
conducted by hypothesis tests and fit of parametric concentrationresponse
models. However, as mortality occurred in exposed snails,
these analyses require to be refined, particularly in avoiding bias that
exists when the number of clutches/eggs is analysed without accounting
for mortality, or when replicates where mortality occurred are excluded;
in the latter case, a number of organisms are discarded and valuable data
can be lost. In this context, the purpose of our statistical study was
twofold. First, we refined the statistical analyses of reproduction data
accounting for mortality all along the test period. The variable “number
of clutches/eggs produced per individual-day” was used for EC
x modelling, as classically done in epidemiology in order to account for
the time-contribution of each individual to the measured response.
Furthermore, the combination of a Gamma-Poisson stochastic part with
a Weibull concentration-response model allowed accounting for the
inter-replicate variability. Second, we checked for the possibility of
optimizing the initial experimental design through the reduction of
exposure duration and/or number of replicates. Based on the six
datasets, we show that using the ‘per individual-day’ unit in ecotoxicology
avoids the exclusion of data (as a consequence the ECx could be not
estimated from remaining data) and ensures an unbiased reproduction
data analysis when mortality occurs in exposed animals. We also show
that the experimental design may be optimized, depending on what
should be prioritized. Even if further studies would be necessary with
other kinds of compounds, we illustrate the fact that, in the case of
cadmium, and if 6 replicates are kept, a 35-day exposure duration would
be sufficient to characterize the toxicity. In the same way, 3-4 replicates
appear sufficient if the exposure duration stays at 56 days. However,
before the reproduction test with L. stagnalis can be standardized, other
works are necessary to furtherrefine the experimental design, e.g., by
regarding exposure duration and replication simultaneously.
Publikationsdato20. maj 2013
StatusUdgivet - 20. maj 2013
BegivenhedSETAC Europe 23rd meeting - Glasgow, Storbritannien
Varighed: 12. maj 201316. maj 2013
Konferencens nummer: 23


KonferenceSETAC Europe 23rd meeting


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