Chlorinated fatty acids contribute to the major portion (up to 90%) of the previously unidentified, extractable organically bound chlorine in fish. Chlorinated fatty acids can be found in storage fat (triacylglycerols) of fish as well as in the membrane lipids (phospholipids). Short-chain, chlorinated fatty acids may be the result of chain shortening via β-oxidation in fish or its prey organisms. However, dichloromyristic acid appears to be resistant to further degradation. Chlorinated fatty acids can be formed in industrial processes (such as chlorination in pulp bleacheries), but natural production cannot be ruled out. Chlorinated fatty acids show low acute toxicity to rat. Several studies, however, indicate that they might have a negative influence on reproduction processes.