|Seawater contains approximately 0.5-2 ppb of nickel, and rivers contain approximately 0.3 ppb. Phytoplankton contains 1-10 ppm nickel (dry mass), resulting in a 103-104 bioconcentration factor compared to seawater. Bentic algae can be found both in freshwater and salt water, and may contain between 0.2 and 84 ppm nickel. Lobsters contain 0.14-60 ppm nickel, molluscs 0.1-850 ppm, and fishes between 0.1 and 11 ppm (all values based on a dry mass). Nickel occurs in water as Ni2+ (aq) and sometimes as NiCO3. It may be either dissolved, or complexed with inorganic ligands. Nickel may also be bound to particles. |
In what way and in what form does nickel react with water?
Under normal conditions nickel does not react with water.
Solubility of nickel and nickel compounds
Elementary nickel is water insoluble at T=20oC pressure = 1 bar. However, nickel compounds may be water soluble. Nickel chloride is most water soluble; 553 g/L at 20oC, to 880 g/L at 99.9oC. Nickel carbonate has a water solubility of 90 mg/L, whereas other nickel compounds, such as nickel oxide, nickel sulphide and nickel tetra carbonyl are water insoluble.
Why is nickel present in water?
Nickel may be found in slate, sandstone, clay minerals and basalt. The main nickel source is pentlandite. The element accumulates in sediments and is a part of various biological cycles.
Nickel may end up in water from both point and non-point sources. Diffuse nickel emissions may stem from power plants, waste incinerators and metal industries. Nickel is directly emitted from various industries through discharge on surface waters. It is applied in alloys for treatment of heavy metal polluted surface water, in nickel-cadmium batteries, as a catalyzer and as a pigment. Pure nickel is often applied as a protective coating on steel and copper objects. Nickel-copper alloys have been applied in coins for a very long time. Other alloys are applied for kitchen ware, jewelry and turbine production. Nickel may be applied as an anti-corrosive. Nickel acetate is applied as a mordant in textile printing, and nickel carbonate is applied as a catalyzer for fat hardening and for ceramic paint production, as is nickel chloride. Nickel tetra carbonyl is a by-product of nickel cleansing and is applied in various production processes.
Nickel compounds are also applied in agriculture. Phosphate fertilizers contain traces of nickel. Nickel is often present in agricultural soils situated near fossil fuel industries. Organic matter often adsorbs nickel, causing coal and oil to contain traces of the element. Nickel compounds may also be found in sludge, and in slags and fly ashes from waste incinerators. Better waste separation would prove useful, because nickel is up to 60% recyclable.
What are the environmental effects of nickel in water?
Nickel is a dietary requirement for many organisms, but may be toxic in larger doses. Metallic nickel and some other nickel compounds are teratogenic and carcinogenic to mammals. Nickel concentrations in plants are usually 1 μg/g, and concentrations above 50 μg/g are toxic. Tea has an extraordinary nickel content of 7.6 mg/kg dried leaves. Nickel causes growth restraints in algae at concentrations of between 0.5 and 10 ppm. Fishes apparently are less susceptible to nickel, but this differs between species. For Daphnia hyaline the LD50 for 48 hours is 1.9 ppm. Chronic nickel toxicity for Daphnia magna lies between 30-150 ppb. The LD50 for marine lobsters lies between 150 and 300 ppm. In the organs of birds mainly living off water organisms nickel concentrations of 0.6-36 ppm (dry mass) were found. Nickel accumulation in rats mainly occurs in lungs, where concentrations exceed those in other organs by 4-40 times.
There are approximately 70 species of plants that accumulate extraordinarily high nickel concentrations. This may be up to 10,000 ppm (dry mass). For regular plant seed 0.5-2 ppm nickel in liquid substrates is considered toxic. Most plants have a relatively high nickel tolerance, but many species of grain are generally more susceptible. When water with a 40 ppm nickel concentration is added these grains may die. Liming of the soil may rapidly decrease nickel uptake. On the other hand, high nickel concentrations may throng other heavy metals. Sludge containing more than 200 ppm nickel (dry mass) may not be applied to agricultural soils.
The five naturally occurring nickel isotopes are all stable. Eight other isotopes are considered instable.
What are the health effects of nickel in water?
The human body contains approximately 10 mg nickel. Nickel is a dietary requirement for a number of organisms, therefore it might be of significance to humans. The human dietary need is estimated at only 5 μg, which is the result of a 150 μg intake. Nickel probably has a function in urea to ammonia conversion by the urease enzyme. Nickel cannot be resorbed in the digestive gland, unless it is complexed.
Nickel inhalation poses a greater risk than nickel in water. This may cause lung cancer, or nasal tumors. Nickel carcinogenity is probably caused by nickel replacing zinc and magnesium ions on DNA-polymerase. These observations were mainly made in nickel working employees. Usually only smoking may cause this problem.
Many people develop dermatitis upon skin contact with nickel. The same goes for nickel solutions. Nickel allergies are more common among women than among men. Nickel compounds may be toxic in high concentrations, but these are often water insoluble, limiting potential harm. For example, nickel tetra carbonyl is water insoluble, but is toxic and carcinogenic nevertheless.
Upon intake of higher doses of nickel one usually vomits, resulting in rapid removal from the body.
Which water purification technologies can be applied to remove nickel from water?
Nickel may be removed from water by means of active carbon adsorption. Coagulation is another feasible option. Nickel only fully precipitates under certain conditions, namely a pH value of at least 9.5, under which it is fully converted to nickel hydroxide.
Literature and the other elements and their interaction with water