Statistical considerations, targets and background variability for exposure assessment. To establish the baseline variability of the DNA adductome for a target tissue/species (and, possibly, a population), replicate samples of single specimens for each assessment site are needed. Based on our experience with amphipods, about 15-20 individuals per site are sufficient when only females in the reproductive stage are considered \cite{Gorokhova2020}. However, species with a larger or lower inter-individual variability in unimpacted sites may require a larger sample size.
Before evaluating data in relation to the contaminants and other health parameters, some QC checks are conducted, using, e.g., Principal Component Analysis (PCA) as a checkpoint to screen for outlier data points and obtain a global perspective of the data \cite{Anwardeen2023}. All single adducts are evaluated for variability and those showing less than 1 % variation across the samples are omitted from the further analyses. Also, adducts that are present in less than 5 % of the samples are omitted.
The data are evaluated using two-tier diagnostics with standard multivariate approaches for omics data \cite{Brereton_2021}