| http://www.w3.org/ns/prov#value | - High levels of mercury in tuna and swordfish, for example, have been shown to have natural sources; the most dramatic effects of oil spills have proved to be localized and relatively transient; and heavy metal contamination, except for lead and mercury, has been found to be highly localized and has relatively minor impacts except at high concentrations.There are, however, other continuing concerns
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