My comments are based on my observations of the lead author’s fieldwork in 2014 at one of their four sites while I was working with the non-profit E-Tech International as their toxicologist, and on my professional judgement from 25 years as a research biologist investigating the exposure and effects of contaminants on aquatic species for the US Geological Survey. My concern is that the quality of the samples may have been compromised by the authors’ field procedures, which would thereby call into question the reported liver Pb concentrations. Appropriate and verified protocols for tissue collection and preservation are essential before contaminants analysis if the results are to be considered reliable. Details on the procedures Cartró-Sabaté et al. used for collecting and preserving the livers are sparse “(hunters) collected and preserved livers from 315 hunted preys individually in buffered 4% formaldehyde solution (v/v). Liver samples were transported at ambient temperature in formaldehyde and placed in a freezer on arrival at the laboratory”. This is especially concerning because the preservation of tissues in formaldehyde is not a recommended method for elemental tissue analysis2