Effects of Common Cooking Methods on Total Mercury and Methylmercury in Sardines and Sprats

The effects of household cooking on mercury speciation in whole small pelagic fish remain insufficiently understood. To address this gap, total mercury (T-Hg), methylmercury (MeHg), and Hg(II) were determined in wet whole-fish homogenates, including viscera, of sardines and sprats before and after boiling, steaming, baking, and frying. T-Hg was determined by AMA-254 and mercury species by HPLC-ICP-MS; results were expressed on wet-weight (ww), dry-weight (dw), and 100 g reference-portion bases. Frying yielded the highest dry matter, underscoring moisture-related differences among reporting bases. T-Hg concentrations ranged from 0.0518 to 0.1322 µg/g dw and MeHg from 0.0273 to 0.0624 µg/g dw. MeHg was detected in all samples, whereas Hg(II) exceeded the method detection limit only in baked and steamed sardines. MeHg amounts per 100 g ranged from 1.38 to 2.35 µg in sardines and from 0.95 to 1.79 µg in sprats. Within the tested batch, no treatment consistently reduced T-Hg or MeHg across both species. By combining analysis of the complete fish matrix with direct mercury speciation and multiple reporting bases, this study provides a food-relevant framework for interpreting mercury in processed small pelagic fish.