Nickel can be nasty

Nickel can poison whole communities and environments. No place on earth suffers from nickel pollution like the industrial town of Monchegorsk in the Murmansk region of north-west Russia where its mining and refining sustains the town's economy. Its inhabitants have a particularly high incidence of respiratory and lung diseases caused by breathing the polluted pall of nickel-laden smoke that hangs over the town. The local environment is blighted with grassless fields and leafless trees poisoned by this element.

Toxic though it is, nickel appears to be an essential element for humans, but we may only need as little as 5 ^g/day. Why nickel is required, and why our bodies retain about 15 mg of this metal, is still not clearly understood, although in some species it is related to growth. The average daily intake is estimated to be around 150 ^g. Canned baked beans provides a meal rich in this element because one of the enzymes of the bean from which this delicacy is made is the Jack bean urease enzyme, containing 12 nickel atoms per molecule. Another rich source of nickel is tea.

It may be essential, but nickel causes problems when in contact with the human body. These problems are of three kinds depending on the form in which we encounter it: touching the metal or its alloys; ingesting one of its soluble salts; or breathing its dust or nickel carbonyl vapour. Actual contact with the metal, or an alloy such as stainless steel, can cause contact dermatitis which manifests itself as 'nickel itch'. People who are susceptible to this are advised to avoid wearing things made of stainless steel such as watches, garment fasteners, spectacle frames, and ear rings. Previous generations of women who wore stockings held up with suspenders became allergic to their metal fastenings, which were invariably made of stainless steel and millions suffered this way, primarily because it transpires that 10% of women are sensitive to nickel. (Only one man in a hundred is affected.)

The other threats from nickel are to those who work with the metal or solutions of its salts in industry. Epidemiological studies show increased risk of lung and nasal cancer among nickel refinery workers and even among those who left the industry many years ago. The reason is thought to be due to nickel atoms substituting for zinc and magnesium atoms in the key enzyme DNA polymerase, which is involved in replicating our individual DNA. The nickel ion is slightly different and so affects the behaviour of this enzyme resulting in the formation of a rogue sequence of DNA and a cancerous cell.

Once it enters the body, nickel binds itself to albumin and is transported via the blood to certain organs where it tends to accumulate, such as the kidneys, the liver, and the lungs. It is excreted primarily via the urine. Fatal poisoning by nickel compounds is extremely rare although a 2-year-old child who ate 15 g of nickel sulphate crystals died within four hours. A group of people on kidney dialysis machines suffered extreme toxic symptoms when a nickel salt was accidentally added to the solution they were being dialysed with. They survived. Nickel salts may be deadly but they are not on sale to the public and as far as can be ascertained, no one has ever used them as homicidal agents.

The deadliest form of nickel is nickel carbonyl, a compound that caused several deaths among workers at a nickel refinery in Wales before its dangers were appreciated. The compound came to light in 1888 when the industrialist Ludwig Mond and his assistant, Carl Langer, investigated the problem of leaky valves through which carbon monoxide gas (CO) was passing. They discovered that the gas was reacting with the nickel from which the valves were made and forming volatile nickel carbonyl, Ni(CO)4, a liquid which boils at 43°C, and which has a musty, sooty odour. From this they developed a process, the Mond Nickel Process, for making very pure nickel but, when it was put into production, there were sudden and unexplained deaths among those operating the plant.

A few breaths of nickel carbonyl vapour will immediately cause a painful throat and tight chest. The person affected soon develops a headache, feels sick, and becomes dizzy. If exposure is brief then these symptoms will clear up after a few days. This apparent recovery may still happen if the person has been heavily exposed to the vapour, but then more serious symptoms begin to appear a week or so later with the lungs being especially badly affected. In such cases the risk of dying is high.

One of the most remarkable cases of nickel carbonyl poisoning happened in 1957 and was of a 25-year-old man who was accidentally sprayed with it and quickly became breathless and started to turn blue. First aid was administered in the form of pure oxygen gas and he was given the antidote diethyl-dithiocarbamate (DDC) and rushed to hospital where his urine showed one of the highest levels of nickel ever recorded: 2 ppm. Because he was given immediate treatment he eventually survived and made a full recovery. There have been cases in which the level of nickel in the urine has been much less where the person has died, and one man with 0.5 ppm succumbed despite being given DDC.

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