A study of lipid- and water-soluble arsenic species in liver of Northeast Arctic cod (Gadus morhua) containing high levels of total arsenic

Abstract

In the present study liver samples (n=26) of Northeast Arctic cod (Gadus morhua), ranging in total arsenic concentrations from 2.1 to 240mg/kg liver wet weight (ww), were analysed for their content of total arsenic and arsenic species in the lipid-soluble and water-soluble fractions. The arsenic concentrations in the lipid fractions ranged from 1.8 to 16.4mg As/kg oil of liver, and a linear correlation (r2=0.80, p<0.001) was observed between the total arsenic concentrations in liver and the total arsenic concentrations in the respective lipid fractions of the same livers. The relative proportion of arsenolipids was considerably lower in liver samples with high total arsenic levels (33–240mg/kg ww), which contained from 3 to 7% of the total arsenic in the lipid-soluble fraction. In contrast liver samples with low arsenic concentrations (2.1–33mg/kg ww) contained up to 50% of the total arsenic as lipid-soluble species. Arsenic speciation analysis of the lipid-soluble fractions of the livers, using reversed-phase high performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (HPLC–ICP-MS), revealed the presence of several arsenolipids. Three major arsenic-containing hydrocarbons (C17H39AsO, C19H41AsO and C23H37AsO) and five arsenic-containing fatty acids (C17H35AsO3, C19H39AO3, C19H37AsO3, C23H37AsO3 and C24H37AsO3) were identified using HPLC coupled to quadrupole time-of-flight mass spectrometry (qTOF-MS). Arsenobetaine was the major arsenic species in the water-soluble fraction of the livers, while dimethylarsinate, arsenocholine and inorganic arsenic were minor constituents. Inorganic arsenic accounted for less than 0.1% of the total arsenic in the liver samples.