Using mercury isotopes to understand the bioaccumulation of Hg in the subtropical Pearl River Estuary, South China

•Hg isotopic compositions in wild fish from subtropical south China showed different patterns.•Small Δ199Hg values in fish indicate less photo-degradation of MeHg before entering the food web.•Significant differences of Δ199Hg values among different species of fish show different feeding guilds.

Coastal and estuarine regions are important areas of mercury pollution. Therefore, it is important to properly characterize the sources and bioaccumulation processes of mercury in these regions. Here, we present mercury stable isotopic compositions in 18 species of wild marine fish collected from the Pearl River Estuary (PRE), south China. Our results showed variations in mass-independent fractionation (Δ199Hg: +0.05 ± 0.10‰ to +0.59 ± 0.30‰) with a Δ199Hg/Δ201Hg of ∼1.26, suggesting that aqueous MeHg underwent photo-degradation prior to incorporation into the food chain. For the results, we discovered small but significant differences of Δ199Hg values among herbivorous, demersal, and carnivorous fish, indicating that different feeding guilds of fish may have incorporated MeHg with various degrees of photo-demethylation. The consistent mercury isotope compositions between fish feeding habitat and mercury sources in the estuary provide potentially important findings on the transformation and bioaccumulation of this toxic metal in subtropical coastal environments.