Nickel is a ubiquitous trace metal and occurs in soil, water, air, and in the biosphere. The average content in the Earth's crust is about 0.008%. Levels in natural waters have been found to range from 2 to 10 µg l^-1 (fresh water) and from 0.2 to 0.7 µg l^-1 (marine). The prevalent ionic form is nickel (II) (WHO 1991).

Most nickel is used for the production of stainless steel and other nickel alloys with high corrosion and temperature resistance. Nickel alloys and nickel platings are used in vehicles, processing machinery, armaments, tools, electrical equipment, household appliances, and coinage. Nickel compounds are also used as catalysts, pigments, and in batteries. The primary sources of nickel emissions into the ambient air are the combustion of coal and oil for heat or power generation, the incineration of waste and sewage sludge, nickel mining and primary production, steel manufacture, electroplating, and miscellaneous sources, such as cement manufacturing. Nickel from various industrial processes and other sources finally reaches waste water. Residues from waste-water treatment are disposed of by deep well injection, ocean dumping, land treatment, and incineration (WHO 1991).

Entry into the aquatic environment is by removal from the atmosphere, by surface run-off, by discharge of industrial and municipal waste, and also following natural erosion of soils and rocks. In rivers, nickel is mainly transported in the form of a precipitated coating on particles and in association with organic matter.

Concentrations of nickel have been measured in water and sediments as part of the National Monitoring Programme at sites throughout the UK in estuaries and coastal waters (MPMMG 1998). The results of the National Monitoring Programme are summarised in Appendix D. MPMMG (1998) should be consulted for more details.

Grimwood and Dixon (1997) compiled monitoring data for nickel in water, sediments and biota for marine sites of nature conservation importance in England.

As an example of the levels of dissolved nickel in the marine environment, the following concentrations have been reported by DETR (1998) for some English estuaries (see tables below).

Nickel occurs in aquatic systems as soluble salts adsorbed on clay particles or organic matter (detritus, algae, bacteria), or associated with organic particles, such as humic and fulvic acids and proteins. Absorption processes may be reversed leading to release of nickel from the sediment (WHO 1991).

Minimum concentration (µg l^-1) of nickel in the water column of some English estuaries (from DETR 1998)

Average concentration (µg l^-1) of nickel in the water column of some English estuaries (from DETR 1998)

Maximum concentration (µg l^-1) of nickel in the water column of some English estuaries (from DETR 1998)

The fate of nickel in freshwater and sea water is affected by several factors including pH, pE, ionic strength, type and concentration of organic and inorganic ligands, and the presence of solid surfaces for adsorption.

An exhaustive literature review on the toxicity of nickel to marine organisms has not been carried out for the purposes of this profile. The information provided in this section is taken from existing review documents (Mance and Yates 1984, Hunt and Hedgecott 1992 and Grimwood and Dixon 1997). The most sensitive groups of organisms have been identified.

Nickel toxicity in aquatic invertebrates varies considerably according to species and abiotic factors. Mance and Yates (1984) reviewed data on the toxicity of nickel to saltwater organisms and found considerable variation of the sensitivity of marine fauna.

The authors proposed an EQS (for the protection of saltwater life) of 30 µg l^-1 (expressed as a dissolved annual average concentration) which is currently adopted in UK legislation (HMSO 1989). The EQS was established by applying an arbitrary factor of 5 to a chronic effect concentration of 141 µg l^-1 found to cause significant effects on spawning in the mysid shrimp Mysidopsis bahia. However, following a review of more recent toxicity data, Hunt and Hedgecott (1992) proposed a more stringent EQS to DoE of 15 µg l^-1. This value (also expressed as a dissolved annual average) was derived by applying a safety factor of around 10 to the same data as that used by Mance and Yates (1984).

Hunt and Hedgecott (1992) also reported effect concentrations ranging from 0.6 - 9 and 10 - 20 µg l^-1 for certain sensitive species of algae and molluscs. However, the studies from which these data were taken were considered to be too unreliable for EQS derivation. Nevertheless, further research into algal and mollusc sensitivity was recommended.

A further review by Grimwood and Dixon (1997) on the toxicity data following the study by Hunt and Hedgecott (1992) found no reliable toxicity data that indicated higher sensitivity of saltwater organisms had been reported for nickel. Grimwood and Dixon recommended that the revised EQS of 15 Fg l^-1 (dissolved annual average) proposed by Hunt and Hedgecott was appropriate for the protection of all saltwater life in the majority of cases. However, as suggested by Hunt and Hedgecott (1992), they stated that where there was concern that the health of communities in sites of nature conservation importance may be compromised as a result of the presence of particularly sensitive algal or mollusc species, a lower value may be used as a guideline. However, in the absence of any new toxicity data, it was not possible to make any recommendations on such a value. This is particularly pertinent considering that if the EQS is decreased further, the value would be at a level close to background concentrations.

Nickel is known to accumulate in sediments but no Canadian interim marine sediment quality guideline was set for nickel in 1999.

Laboratory studies have shown that nickel had little capacity for accumulation in all the fish studied. In uncontaminated waters, the range of concentrations reported in whole fish (on a wet-weight basis) ranged from 0.02 to 2 mg kg^-1. These values could be up to 10 times higher in fish from contaminated waters. In wildlife, nickel is found in many organs and tissues due to dietary uptake by herbivorous animals and their carnivorous predators. However, accumulation factors in different trophic levels of aquatic food chains suggest that biomagnification of nickel along the food chain, at least in aquatic ecosystems, does not occur (WHO 1991).

Potential effects include:

• acute toxicity to algae and invertebrates (in particular molluscs) at concentrations in the water column of dissolved nickel above the proposed EQS of 15 µg l^-1 (annual average) of dissolved nickel.

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