Subcellular Cadmium, Lead and Mercury Compartmentalization in Guiana Dolphins (Sotalia guianensis) From Southeastern Brazil

Rachel Ann Hauser-Davis,Rafael C C Rocha,Leila Lemos,Lívia Figueiredo,Roberta L Ziolli,Tatiana Saint’Pierre,Salvatore Siciliano,Jailson Fulgêncio De Moura

doi:10.3389/fmars.2020.584195

Abstract

Marine mammals are considered excellent ocean health sentinels and are ubiquitously exposed to chemical contaminants worldwide. The Guiana dolphin (Sotalia guianensis) is a near-threatened dolphin species from Brazil with unknown population size data. This indicates the need for assessments regarding deleterious effects that may arise from exposure to chemical contamination, especially metals. After entry in the organism, these compounds are subject to internal subcellular compartmentalization, which in turn alters their bioavailability. However, almost no assessments regarding subcellular metal contents in marine mammals are available. In this context, metal compartmentalization was determined in three subcellular fractions for three toxic elements, Cd, Hg and Pb, by inductively coupled plasma mass spectrometry (ICP-MS) in Guiana dolphin kidney and liver samples from Southeastern Brazil. Differential metal-detoxification mechanisms were observed for the three elements, where metallothionein (MT) detoxification was postulated for only for Pb, while Cd and Hg were poorly associated to MT, and mostly present in the insoluble fraction, indicating low bioavailability. This is the first report on subcellular metal compartmentalization in Guiana dolphins and indicates that critical biochemical detoxification data is obtained through subcellular fraction analyses in marine mammals. This indicates an emerging study field for this type of assessment, which may, in turn, aid in conservation efforts.

Highlights

Metal and metalloid contamination in aquatic ecosystems is a growing concern worldwide, since these elements may lead to potential toxic effects and display the ability to bioaccumulate and/or biomagnify throughout the trophic web (Censi et al, 2006)
Cd in kidney and liver was mostly concentrated in the insoluble fraction, with the heat-denaturable and heat-stable fractions
This indicates that non-bioavailable concentrations of this element, and that the MT detoxification pathway does not seem to be induced by Cd levels in the evaluated Guiana dolphin specimens

Summary

Introduction

Metal and metalloid contamination in aquatic ecosystems is a growing concern worldwide, since these elements may lead to potential toxic effects and display the ability to bioaccumulate and/or biomagnify throughout the trophic web (Censi et al, 2006). After entry in the organism, metals and metalloids undergo internal subcellular compartmentalization, which alters their bioavailability, and, potential deleterious effects. Metals and metalloids present in soluble cellular fractions are bioavailable and may lead to toxic cellular effects while insoluble metals are inert and, biologically unavailable (Wallace et al, 2003; Dragun et al, 2015). Organisms utilize several detoxifying pathways in order to remove these contaminants from the body, where detoxification proteins [such as metallothionein (MT), MT-like proteins and glutathione] and enzymes are present mainly in the soluble cellular fraction, while insoluble fractions contain metal-rich granules, organelles, and cellular debris (Wallace et al, 2003; Marijicet al., 2016)

Methods

Results

Conclusion