Analysis of persistent halogenated hydrocarbons in fish feeds containing fish oil and other alternative lipid sources

A trade-off exists between beneficial n-3 long-chain polyunsaturated acids and toxic persistent halogenated hydrocarbons (PHHs), both of which primarily originate from fish oil commonly used in fish feeds. Alternative lipid sources are being investigated for use in fish feeds to reduce harmful contaminant accumulation, hence, research is needed to evaluate PHHs in fish feeds with various lipid compositions. An analytical method was developed for PHHs including nine organochlorine insecticides (OCPs), 26 polychlorinated biphenyls (PCBs) and seven polybrominated diphenyl ethers (PBDEs) in fish feeds with differing proportions of fish oils and alternative lipid sources by GC-ECD after accelerated solvent extraction, gel permeation chromatography (GPC), and sulfuric acid cleanup. The GPC removed the majority of the neutral lipids and sulfuric acid treatment effectively destroyed the polar lipids. Thus, the combination of the two methods removed approximately 99.7% of the lipids in the extracts. The method detection limits were less than 5 ng/g dry weight (dw) for most PHHs, while recoveries were 75-118%, 67-105%, 69-92%, 63-100% and 94-144% with relative standard deviations of 0.2-39%, 0.3-20%, 0.5-12%, 1.5-18% and 1.5-15% for PHHs in five types of fish feeds made from different lipid sources. Although the source of lipid showed no impact on cleanup efficiency and the developed method worked well for all feeds, fish feeds with 100% fish oil contained background PHHs and more interference than feeds containing alternative lipids.