Vulpes vulpes_tissue composition_Total mercury

This data set concerns the tissue composition (water and lipid proportions) and total mercury in wet, dry and dry-lipid extracted form for red fox tissues (Vulpes vulpes), collected between 2012 and 2020. Contaminant concentrations in wildlife toxicology studies are inconsistently expressed in wet or dry mass units, or even on a lipid-normalized basis, but tissue composition is rarely reported, and the conversion between dry and wet mass units, notably, is often based on assumed empirical moisture contents in tissues. However, diverse factors (e.g., tissue, storage conditions) may affect tissue composition and render comparisons between studies difficult or potentially biased. We used these data as an illustration, to quantify the effects of diverse variables on moisture and lipid contents and their consequences on contaminant concentration in different tissues, when converting between wet and dry mass units (lipid extracted or not). We found that moisture content differed largely between organs, enough to preclude the use of a single conversion factor, and decreased rapidly yearly by 1% when stored in a -80°c freezer. Although most fox tissues have low lipid concentrations, lipid content affected water content and their extraction affected the wet to dry mass conversion factor. We thus recommend reporting tissue composition (at least water and lipid contents) systematically in toxicology studies and using tissue/species specific conversion factors to convert between dry and wet mass concentration.