Tại châu Âu, niken (Ni) được liệt kê II Danh sách Ủy ban châu Âu (các chất nguy hiểm Chỉ thị) và quy định thông qua Hội đồng Cộng đồng châu Âu bởi vì độc tính của nó, kiên trì, và mối quan hệ tích lũy sinh học (Bubb và Lester 1996). Tại Canada, niken và các hợp chất có trong Danh mục các chất ưu tiên theo Đạo luật bảo vệ môi trường Canada (Hughes et al. 1994). Tổ chức Y tế Thế giới (WHO) phân loại các hợp chất niken trong Nhóm 1 (con người chất gây ung. | CHAPTER 6 Nickel INTRODUCTION In Europe nickel Ni is listed on European Commission List II Dangerous Substances Directive and regulated through the Council of European Communities because of its toxicity persistence and affinity for bioaccumulation Bubb and Lester 1996 . In Canada nickel and its compounds are included in the Priority Substances List under the Canadian Environmental Protection Act Hughes et al. 1994 . The World Health Organization WHO classifies nickel compounds in Group 1 human carcinogens and metallic nickel in group 2B possible human carcinogen . Public Health Service USPHS 1993 . The . Environmental Protection Agency USEPA classifies nickel refinery dust and nickel subsulfide as Group A human carcinogens USPHS 1993 and nickel oxides and nickel halides as Class W compounds that is compounds having moderate retention in the lungs and a clearance rate from the lungs of several weeks USEPA 1980 . Nickel and its compounds are regulated by USEPA s Clean Water Effluent Guideline for many industrial point sources including the processing of iron steel nonferrous metals and batteries timber products processing electroplating metal finishing ore and mineral mining paving and roofing paint and ink formulating porcelain enameling and industries that use process or manufacture chemicals gum and wood or carbon black USPHS 1993 . Nickel is ubiquitous in the biosphere. Nickel introduced into the environment from natural or human sources is circulated through the system by chemical and physical processes and through biological transport mechanisms of living organisms National Academy of Sciences NAS 1975 Sevin 1980 WHO 1991 . Nickel is essential for the normal growth of many species of microorganisms and plants and several species of vertebrates including chickens cows goats pigs rats and sheep NAS 1975 USEPA 1980 WHO 1991 USPHS 1993 1995 . Human activities that contribute to nickel loadings in aquatic and terrestrial ecosystems include mining smelting
