Zinc stable isotopes in mangrove crabs as tracers of anthropogenic contamination in a tropical estuary

Our study presents a novel approach for tracing anthropogenic zinc (Zn) bioaccumulation in mangrove crabs using Zn stable isotope compositions (δ⁶⁶Zn). We analyzed δ⁶⁶Zn and elemental composition in crab tissues from Brazilian mangroves within a coastal lagoon historically impacted by electroplating waste. Crabs from the mangrove area near the old electroplating plant exhibited the highest Zn concentrations in both muscle and hepatopancreas, likely reflecting the high Zn bioavailability in these sediments. In contrast, crabs from other mangrove sites showed minimal variations in Zn concentrations, despite prominent differences in sediment Zn levels. This suggests that crabs regulate their internal Zn concentrations within a specific range, not correlating with external Zn bioavailability. The tissues of crabs from contaminated sites bore heavier δ⁶⁶Zn, consistent with the δ⁶⁶Zn left by industrial Zn pollution in sediments. However, δ⁶⁶Zn did not correlate directly with either bioaccumulated Zn or sediment Zn levels, making it challenging to distinguish between stations with varying contamination degrees. Shifting δ⁶⁶Zn in crab tissues toward lighter isotopes compared to sedimentary Zn indicates the influence of diet, internal biological fractionation, specific bioaccumulation pathways, or additional Zn sources. Biological fractionation within crabs likely caused muscle tissues to be isotopically lighter than the hepatopancreas, especially in moderately contaminated areas. This first systematic study of δ⁶⁶Zn within mangrove crabs highlights the need for further research to fully understand isotopic variations in crab tissues and their relationship with environmental, ecological, and physiological factors. Initial findings suggest that sources, bioaccumulation routes, and regulatory mechanisms shape δ⁶⁶Zn within crab tissues.