Assessment of clinical outcomes associated with mercury concentrations in harbor seal pups (Phoca vitulina richardii) in central California

Monomethyl mercury (MeHg+) from the diet can cause mild to severe neurotoxicosis in fish-eating mammals. Chronic and low-level in utero exposure also can be neurotoxic, as documented in laboratory animal studies and epidemiologic investigations. In free-ranging animals, it is challenging to study low-level exposure related neurotoxicosis, and fewstudies have investigated the relationship between mercury (Hg) and adverse outcomes inwild populations. Relative to Hg concentrations on admissionwe evaluated different types of behaviors for 267 Pacific harbor seal (HS; Phoca vitulina richardii) pups at The Marine Mammal Center from 2015 to 2019 during rehabilitation after stranding and maternal separation. Admitted HS pups underwent a clinical exam; including sex and weight determination, and hair (partly lanugo grown in utero) and blood samples were collected for total Hg concentration ([THg]) determination. All pups weremonitored weekly (behavior assessments included response to tactile stimulation, movement, swimming, interactions with other seals, hand feeding, and feeding independently), and days in rehabilitation and survival were recorded. There was a significant negative correlation between [THg] and responses to tactile stimulation andmovements, measured in both hair andwhole blood (p < 0.05). This relationshipwas found both during the intensive care unit (ICU) stage, and during the pool stage of rehabilitation. Additionally, there was a significant association between greater [THg] and number of days spent in rehabilitation, although there was no relationship between [THg] and survival. There was a significant sex difference, with greater [THg] in female pups, which contrasts with previously published findings in juvenile and adult harbor seals. Our findings support small, but significant associations between gestational THg exposure and clinical effects for tactile sensory response and movement, and longer rehabilitation durations for HS pups, although there was considerable variability among animals. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The study found important associations between low-level exposure to monomethyl mercury and behavior as well as rehabilitation time in harbor seal pups. Specifically, a significant negative correlation was found between total Hg concentration and responses to tactile stimulation and movements during both the intensive care unit (ICU) stage and pool stage of rehabilitation. Additionally, a significant sex difference was observed, with female pups showing higher total Hg concentrations compared to male pups.