About 1500 different HHCs, from simple alkanes to complex polyhalogenates, are produced naturally by a diversity of aquatic and terrestrial organisms in microgram per kilogram body mass levels. Methyl chloride, methyl iodide, and carbon tetrachloride, which are animal carcinogens, occur naturally in marine environment. Several of those produced in large amounts include chlor-omethanes, chlorophenols, and chlorinated humic/fulvic compounds. Largest amounts of these HHCs are produced in soil and sediments. Some of these HHCs include haloperoxidase enzymes, which yield volatile and phenolics. Reactions of chlorine with lignin pulp and humic/fulvic acids produce chloroliginin. Numerous other halogenated hydrocarbons, many structurally similar to known animal carcinogens and toxicants, occur in both terrestrial and marine organisms. Several haloge-nated hydrocarbons are essential for normal functioning of living organisms.
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