Nickel – A Trace Element Hardly Considered

In this paper, occurrence, environmental mobilities and ecological cycling of nickel up to daily intake and allergic reactions of humans is discussed, mainly based on data of the author and others, which are often hidden in multi-element tables, and not available via keywords. Whereas, apart from some hotspots of geology, nickel occurrence in Central Europe is moderate, sources of pollution are mainly smelters and oil production. Oil combustion is likely a main source of nickel pollution in street dust, and after oil spills. Remediation and phytomining may be possible by use of special accumulator plants. Fertilizers do not increase nickel levels in soils. In green plants, nickel levels are much higher than in animal tissues and products of animal origin, and in fungi they are highly variable. From this, vegans have 4-5 times the daily intake compared with mixed diet feeders, which already touches the range of allergic reactions of sensitive persons. Essentiality and toxic effects are also discussed. Keywords— Nickel – environmental occurrence, feeds, food, daily intake, metabolism, toxicity, allergy.

has an affinity towards hematite/magnetite, but not towards CaO/CaSO4-partikels and soot, in particular after combustion of finely ground coal with oxygen at 1400°C (CLARKE 1993).
Mineral constituents can be removed from crude coal by dissolution in oil and subsequent pressure filtration at 45°C (ZIEGLER 2012).
In oil, in particular vanadium, but also nickel, have got enriched, they are therefore regarded as markers from oil combustion.Medium and heavy crude oils as well as high boiling fractions contain high amounts of sulfur and metals, like 10-160 mg.kg -1 Ni, bound to porphyrines.The proportion V/Ni ranges from 10 to 100 and can be used to classify oils and rocks of origin with respect to the period of origin and redox conditions met there, as well as the lithological facies.In oil from Venezuela, crude oils were assigned to 5 groups, and in in each of them, a good correlation between vanadium and nickel could be established (LOPÉZ SALVADOR, MONACO 2017).
In oil, Ni and V are bound to 3 different high molecular fractions.Thermal treatment during oil distillation results in the aggregation of high-molecularweight fractions and thus to enrichment in the residue (DESPREZ ET AL., 2014).During raffination, they remain largely in the residue (asphalt), which contains an average of 336 mg.kg-1 (range 250-500mg.kg - ) Ni and >2000 mg.kg -1 /(range 500-5000 mg.kg -1 ) V. Therefore, asphalt is a main source of Ni in street dust (see chapter "atmosphere and dust").
De-sulfurization of oil by reaction with H2 under pressure and release of the resulting H2S in general also removes Na, V and Ni from the oil-made products (ZIEGLER 2012).
In oil-contaminated soils, high degradation rates of nickel-and vanadiumporphyrines could be established at weak acid pH by combined actions of Bacillus megaterium-Enterobacter cloacae as well as Aspergillus unguis-Penicillium griseofulvum (CORDERO ET AL., 2015).
After the explosion of the oil-drilling platform deepwater horizon, at April 20 th , 2010 in the Gulf of Mexico, 779 million litres of crude oil dissipated within 87 days, which contaminated an area of 75000 km².Whereas the hydrocarbons could be degraded or burnt, the metals dissolved in the crude oil remained on site (V, Ni, Cr), or formed fine dust particles in the course of carburation, which led to enrichment and biomagnification in whales (see chapter about food of animal origin)(WISE ET AL., 2014).

SOILS AND FERTILIZERS
In soils derived from clay rocks, higher nickel levels can be expected, whereas soils derived from carbonaceous rocks usually contain nickel at lower levels.Aqua regia may not release total nickel in all cases, in particular at hotspots.Thus, median nickel for arable topsoils in France has been determined as 21,0 mg.kg -1 in total (4363 samples), and as 19,1 mg.kg -1 (5184 samples) in aqua regia (BAIZE ET AL. 2007).In the UK, a median of total Ni was found at 15,8 mg.kg -1 in arable soils and at 22,0 mg.kg -1 in urban soils.Nickel was slightly higher in Northern Ireland than in England and Wales, some hotspots of geological origin occurred in Scotland (ROSS ET AL. 2007).In Taiwan, however, soils of the Central mountain range contained just 13,2 ± 1,5 mg.kg -1 (KUO ET AL., 2009), possible due to subtropical climate and high precipitation rates, and generally high vertical mobility of nickel in soils (SAGER 2001).In Austria, local enrichments have been found in sedimentites from cretaceous, and above serpentinites (DANNEBERG 1999).The Austrian soil inventory done by aqua regia soil digests found a median abundance of 34 mg.kg -1 for nickel in arable soils (range of medians of various soil types 25-45 mg.kg -1 ) (DANNEBERG 1999).Soils sampled in Vienna city also contained just 30,3 ± 6,3 mg.kg -1 (PLAHL ET AL., 2002).
In Hokkaido (Japan) native green plants contain 20-100 mg.kg -1 Ni in dry mass due to high nickel and low calcium levels met in local soils, which have been developed upon ultramafic rocks, which is more than Cu, and in some cases also more than Zn and Mn.The hyper accumulator Thlaspi japonicum reached top levels of Ni >0,1%, higher than Fe, but without showing toxicity symptoms (HORIE ET AL., 2000).
On behalf of the Council Directive 1999/31/EC on the landfill of waste, and §8 of the Bundesbodenschutzgesetz 1999 (Federal Soil Protection Act), the German government has set thresholds for nickel of 70 mg.kg - for childrens´playgrounds, 140 mg.kg - for habitational areas, 350 mg.kg -1 for sport-and leisure areas, and 900 mg.kg -1 for industrial areas, each determined for dry soil sieved < 2mm digested by aqua regia.In Austria, each province has issued a soil protection act of its own.
In mine tailings, organic carbon, nutrients or soil bacteria are hardly present.In New Caledonia at a mine tailing of 1,8% Ni, prior to planting grass, nitrogen fixing soil bacteria were isolated from the rhizosphere of endemic plants Gymnostoma ebbianum and Serianthus calycina, to modify and amplify their especially Nitolerant genes by molecular genetic methods (HÉRY ET AL., 2005).
Whereas lime addition lowers mobilities and phytotoxicities of most metal ions for arable crops, it increased Ni-uptake into accumulator plants of the Alyssum family.Under various soil pH and Ni concentrations tested, Alyssum murale accumulated up to 1,1% Ni, and Allyssum corsicum up to 0,7% Ni in its dry mass (KUKIER ET AL., 2001; BREWER ET AL., 2001).Also, after NPK fertilization, Alyssum bertolonii accumulated Ni 13400 fold from a Ni-rich substrate, and Berksheya coddii 17000 fold (BROOKS ET AL., 1998).
Mixing of de-watered sewage sludge with equal amounts of sawdust as well as lime gradually increased the water-soluble and exchangeable fractions after 3 months, because of lowering of its pH (ŠČANČAR ET AL., 2001).
After mixing the top 15 cm of various soils with nickel-contaminated urban sewage sludge (4625mg.kg - Ni), elution of nickel with carbonaceous simulated river water from respective soil columns increased significantly.Nickel migrated faster in unsaturated columns, except for the carbonaceous soil, in spite of simultaneous pH increase caused by the sewage sludge.Higher retention from carbonate or organic carbon was achieved only at unsaturated conditions (WELCH, LUND 1987).
Sequential leaching procedures revealed high affinities of nickel towards Mn-oxides and Fe-oxide containing phases, depending on the geochemical matrix (SAGER ET AL., 1989; SAGER, VOGEL 1993).About ¼ or more remained bound to refractory phases, however.In particular at non-contaminated sites, mobility in 0,16M actetic acid and 0,2M oxalate solution remains marginal (SAGER 2016).Amounts readily adsorbed from aqueous solutions are hardly released into neutral or alkaline salt solutions, but almost completely at pH 5 or less, because obviously the hydroxide which gets formed at alkaline surfaces, dissolves (SAGER 1995; ZATKA ET AL., 1992).In acetic acid, tartaric acid or oxalic acid solutions, nickel migrated through clayey barrier layers (Kf about 10 -15 m.s -1 ) quicker the Cd, Cu, and Pb in any case, and frequently even quicker than the acid itself (SAGER 2001).Because nickel levels encountered in fertilizers are usually lower than in soils, accumulations from fertilizations need hardly to be considered (table 1).Fertilization of an equivalent equal to 100 kg P.ha -1 is about equal to the annual atmospheric deposition, and an equivalent of 100 kg N is even less (SAGER 2009).
Also, composts, manures and dungs contain less nickel than arable soils.Thus, urban biowaste of Vienna collected separately within brown tons, contained after pre-selection and sieving an average of 10,46 mg.kg -1 from the center, 17,12 mg.kg -1 from the suburbs, and 14,43 mg.kg -1 from the city border areas, contrary to the urban soils (mainly parks), which had 30,25 mg.kg -1 (PLAHL ET AL., 2002).
Urban biowaste monthly collected at 4 sites of an Austrian provincial capital city, contained even less nickel than compost samples.In outliers due to faulty inputs (2 out of 44 samples), however, nickel concentrations increased 9-fold, thus necessitating control and site selection measures (SAGER 2012).

WATER
A threshold for nickel in potable water at 20 µg.l -1 has been implemented by the Council Directive 98/83/EC after respective recommendation of the WHO.This value applies to a sample of water obtained at the tap and taken so as to be representative of a weekly average value ingested by consumers.
In Cornwall, a known metalliferous and arseniferous region, about 500 private wells have been tested, which were not subject to official control.Traditionally, groundwater was filtrated through 0,45µm, and tap water was analyzed as such, but differences were only noted in case of Pb and Fe.Only 3% of the samples contained Ni above theshold, and were also high in Mn.Sampling of rainwater from roofs is prone to contaminations from the roof material, dust input and organic debris, as well as from microbial activities.Pasteurization in black painted glass tubes by heating from sun rays may cope with the latter.Contact of the chloride containing rain water with a steel pot, however, caused corrosions and subsequently an increase of nickel in the processed water samples (DOBROWSKY ET AL., 2015).
In surface waters, uptake of nickel into algae increased in parallel to the incorporation of C by photosythesis, and correlated non-linearly with the proton flux.In freshwater of pH 7,8 and 12°C, algal nickel uptake was 76% more at light than at dark (GRAY, HILL 1995).
1 g of barley straw can adsorb about 10 mg nickel from aqueous solution, maximum at pH 4,85 (THEVANNAN ET AL., 2010). 1 g of montmorillonite can sorb about 2 mg Ni at pH 5-6, which could be increased by Fe-coatings, but not by Al-coatings (COOPER ET AL., 2002).Aqueous suspensions of lime approach a pH 8-9, resulting in adsorption of Ni, like Pb, Cd, Zn, Cu and Cr(III), at < 90% at the solid.Sorption of Nickel upon finely ground bricks at 80%, and sorption at silicate pebbles at 65% were less effective (AZIZ ET AL., 2008).Fly ash from coal-operated power plants is suitable for the removal of nickel from metal contaminated effluents, e.g. from non-ferrous smelters, which is necessary to save the bacteria of sewage sludge treating processes, which are harmed at Ni > 15 mg.l -1 .The efficiency of fly ash was better than active carbon, but worse than zeolite.Above pH 8,5-9, complete and largely irreversible adsorption at the solids occurred, but none below pH 4,5 (MAVROS ET AL., 1993).
Samples to check pollution from tap water tubings, which may release in particular Cu, Pb, and Ni, are obtained from 1 liter without discarding directly at the consumer´s site (random sampling of the day).If thresholds are surpassed, sequential sampling has to b e done (for Austria: Trinkwasserverordnung 2001, resp.update of the food safety act 2017).Metal water supply tubings, particularly from water heating supplies, can release metals into the potable water, which decrease exponentially versus the consumed water volume (informal measurement of the author).

ATMOSPHERE AND DUST IMMISSION
Apart from antropogenic emissions, the most important source of atmospheric particulates is the weathering of the continental crust.Antropogenic emissions can be easily traced from enrichments over iron.
In the aerosol sampled above the Atlantic Ocean, only < 0,05 -10 ng.m -3 nickel have been found, lowest above the Southern part, and maximum in the Channel (VOLKENING, HEUMANN 1990).In Detroit region within 1988-92, atmospheric nickel concentrations in residential areas were determined as 5-16 ng.m -3 , and in industrial areas 8-32 ng.m -3 .Antropogenic emission sources like vehicles, fuel and navigation remained constant, whereas emissions from smelting and welding facilities varied due to economic fluctuations (PIRONE ET AL. 1995).
Nickel contents in the fine dust of Santiago de Chile (PM10) lowered in winter (July) within the period 1997 -2003 from 60 ng.m -3 to 20 ng.m -3 .Similar concentration decreases appeared also for V, Pb, As, Cu and Cd, which could be traced to lower industrial emissions and lower coal heatings, just Cr increased.Sequential extraction of the dust particles assigned nickel to the group of immobile elements (Ni, Mo, Ca, Mg, Ba, Al) (RICHTER ET AL. 2007).In the Saloniki region, total nickel concentrations in fine dust (PM7,5), samples 1997/98 4m above ground, differed between urban sites at 6,8 ± 5,6 ng.m -3 and sites close to industrial areas at 12,8 ± 6,2 ng.m -3 .Similar effects were observed for Cd, Mn and Zn (VOUTSA, SAMARA 2002).
At hardly populated sites in Norway, metal deposition tends to decrease from the most southern point at Birkenes towards the north, with seasonal fluctuations, but without marked seasonal trends.This atmospheric nickel deposition was calculated from concentrations met in rainwater samples and annual precipitation, to be 1,2 -12 g.ha -1 a -1 (BERG ET AL. 1994), which can be regarded as background immission.
Higher precipitation rates, in parts also as fog, might cause much more total atmospheric deposition in high mountain areas, far away from emission sources.At 2 stations at the Christlumkopf mountain (1768m, Achenkirch, Tirol) close to woods, nickel deposition of 25,02 g.ha -1 a -1 were measured, as the sum of 14,77 g.ha - 1 a -1 wet deposition, only 0,71 g.ha -1 a -1 dry deposition, and 9,54 g.ha -1 a -1 g/ha.afrom the fog.In some distance downhill, at the Mühleggerköpfl, total nickel deposition amounted only 13,62 g.ha -1 a -1 , as the sum of 9,78 g.ha wet, 3,67 g.ha -1 a -1 dry, and only 0,17 g.ha -1 a -1 from the fog (BAUER ET AL. 2008).Top levels of atmospheric nickel deposition of 170-240 g.ha -1 a -1 have been reported from urban districts in Paris, sampled in 1988 (GRANIER ET AL. 1992).Also, the atmospheric deposition at the sea of Tokyo Bight is strongly influenced from human activities.Samples have been obtained by collection of wet precipitation, and for dry deposition by means of a water surface sampler employing circulating 0,25M HCl.Total Ni deposition was 28-98 g.ha -1 a -1 , and the proportion of dry to wet deposition was 3,7 (SAKATA, TANI, TAKAGI 2008).
Contrary to soils, the easily mobilisable fraction of nickel found in street dusts can be about half and thus rather high, which was measured in Sevilla 1996 (FERNANDEZ ESP INOSA ET AL. 2002).
Urban dust samples from the Saloniki urban region contained about 80% of Ni soluble in 0,1M-HCl, which was regarded as labile, contrary to dust samples from the Saloniki industrial region of about 60% soluble in 0,1M-HCl.The solubility in artificial serum was regarded as bioavailable, which was 46% for the urban dust samples, and 24% for the dust close to the industrial areas.The soluble solid phase is presumably NiSO4, and the hardly soluble phase presumably Ni-oxides (VOUTSA, SAMARA 2002).
Occupational exposure from nickel containing dusts occurs especially in the air at the working site of smelters and metal processing facilities.Soluble nickel compounds get rapidly adsorbed by the lung tissues, but the top cancerogen is Ni2S3.To the contrary, in nickel mining no statistically significant relationship between lung cancer and nickel exposition could be established, because the dominant mineral pentlandite [(Ni,Fe)9S8] is non-cancerogenic (SCHAUMLÖFFEL 2012).
Because nickel in coal is bound to sulfides and oxides, fly ash emissions from caloric power plants contain NiSO4, NiS and NiS2, as well as nickel-containing spinels NiFe2O4.but not Ni2S3.High combustion temperatures favour the formation of the oxide, lower temperatures favour the phosphate (SCHAUMLÖFFEL 2012).
Metallic nickel-nanoparticles of 53 nm average diameter, have been obtained by reduction of a NiCl2containing aerosol with H2 at 950°C with 99% yield.Lowering the temperature to 800°C lowered the yield, as well as the average particle diameter to 31 nm (YONG JAE SUH ET AL. 2004).

FUNGI
In general, the composition of soil is of stronger influence upon the contents of mushrooms than upon the composition of green plants, but respective investigations are scarce.In boletus edulis from central Finland, growing upon granitoid rocks, 1,32 mg.kg -1 (of Ni in dry mass) had been found, and from a region higher in nickel from East of Finland, it was 1,55 mg.kg -1 (of Ni in dry mass).The difference between these sites was much larger for Lactarius trivialis, i.e. 0,55 mg.kg -1 resp.1,95 mg.kg -1 (NIKKARINEN, MERTANEN 2004).

FEEDS
Commercially available composite feeds for any kinds of animal contain about 2 mg.kg -1 of Ni.Slightly lower levels in feeds targeted to calves and cats/dogs probably result from higher proportions of meat and dairy products in the composite.Some more differences appear in commercial supplementary feeds, the median level of which is higher for pigs, sows, and piglets, than for cattle, calves, deer, and poultry (table 2).
In basic feeds for dairy cattle, sampled directly at farms in Lower Austria, nickel levels were lowest in

FOOD OF GREEN PLANT ORIGIN
Based on dry mass, food for human nutrition of green plant origin contain some less nickel than food for domestic animals.Just carrots were rather high in Ni (table 3), which needs to be confirmed, however.High levels met in cocoa are known from other references as well.Further sources of nickel intake of human consumption, like nuts, spinach, or mushrooms, have not been investigated in this work.Tea leaves and coffee beans might contain much nickel, which is largely not transferred to the consumed beverage.Contrary to Cd and Pb, traces of Ni are proven to be essential and have a wide range of effects, including plant growth, plant senescence, N metabolism (as a component of urease), and Fe-uptake.In barley (hordeum vulgare), Ni deficiency had been observed after grown for three generations in purified nutrient solution <30 ng/l Ni, resulting in a 15% reduction of optimum yield and Ni in the grains of 90 ± 10 µg.kg -1 dry weight.Ni deficiency inhibited the development of the embryo soon after the formation of the shoot primordia; the root primordia of Ni-deficient grain were poorly developed or absent at harvest (BROWN ET AL. 1987).
Increase of total nickel in soil from 30 to 50 mg.kg - , resp.addition of 35 µg.l -1 in hydroponic culture, did not effect growth of various crops, like spinach (spinacea oleracea), maize (zea mays), beans (phaseolus vulgaris), cabbage (brassica oleracea), rice (oryza sativa), or ryegrass (lolium perenne).All plants investigated contained higher nickel concentrations in their roots than in their shoots, and Ni-additions went preferably to the roots.In the shoots, highest levels were met in beans and ryegrass, and lowest in maize.Due to low root masses, however, about 80% of total Ni contents in beans, cabbage and spinach were located in the shoots (GUO ET AL., 1995).
Additions of soluble NiSO4 to an alkaline soil (pH=8,0 / 14,3% clay/ 5,5% CaCO3) up to 600 mg.kg -1 Ni did not result in Ni uptake proportional to the added amount.Just barley (hordeum vulgare) decreased growth, but cabbage (brassica juncea), spinach (spinacea oleracea), sorghum (sorghum vulgare), beans (phaseolus vulgaris), tomatoes (solanum lycopersicum) and ricinus (ricinus communis) were not effected.Nickel remained mainly in the roots, just in the brassica the excess was transferred to the shoots.Maximum nickel uptake was noted into spinach leaves, and minimum into tomato plants.Top values in edible parts were 65 mg.kg -1 in spinach, 21 mg.kg -1 in beans, 8,1 mg.kg -1 in tomatoes, and in sorghum and barley just 4 mg.kg - , in dry mass each (GIORDANI ET AL., 2005).In case of sufficient NPK fertilization, no toxicity symptoms in pot experiments developed in carrots, potatoes, and onions up to 250µg.l - nickel in irrigation water (equal to 100 g.ha -1 ), because sorption of the soil was quicker than plant uptake (STASINOS, ZABETAKIS 2013).
In case of more saline irrigation, however, like in the delta of the Nile, spinach, maize and leeks retain less nickel (and also cadmium) in the roots, resulting in higher transfer to the leaves, which was traceable in the soil saturation extract (HELAL ET AL., 1998).
Lower nickel levels encountered in white bread from Denmark (median 101 µg.kg -1 ) compared with the level in Austrian wheat (median 255 µg.kg -1 ) can be explained from humidity and the milling fraction of the cereal (LARSEN ET AL., 2002).Similar nickel levels have been found already in 1983 in the FRG, at a median of 228 µg.kg -1 (range 60-1100 µg.kg -1 ).After milling, the white flour made 70% of the total grain weight, but contained just 12% of the entire nickel, the rest was bound to the brans (SCHELLER ET AL. 1988).German wholemeal bread contained 166 µg.kg -1 , which was more than double of conventional mixed bread of 69 µg.kg -1 .Abrasion in the bakery additionally increased nickel in wholemeal bread versus nickel in wholemeal flour.
Because grapes have more than half of their nickel bound to the skin, during wine processing the nickel mainly moves to the residue, and further amounts get adsorbed at the glass bottle.Nickel accumulates preferably in leafy vegetables, cocoa and nuts.Within a compilation from Great Britain about trace elements contents of various food items, maximum nickel was found in nuts to contain 2,5 mg.kg -1 in wet weight (YSART ET AL., 1999).
Tea leaves also contain rather much of nickel, median values from various tea-cropping regions in Asia ranged 1,2 -2,6 mg.kg -1 .But as tea leaves are strong adsorbents, the nickel level in the ready made beverage remains very low (TADAYON, LAHIJI 2011).Also, nickel gets adsorbed on ground coffee within 15 min at 90% in the cold, but just at half at 44°C.For desorption into acid, however, pH 3 is at least needed (SUK, SU 2004).
Though the components for beer brewing contain significant amounts of nickel, like hop with 1,3 mg.kg-1 (range 0,6-2,1 mg.kg -1 ), and malt with 0,11 mg.kg -1 Compared with innards, muscles are low in nickel.Meat products receive their nickel mainly from spices and additives, but not from steel vessels and cans (SCHELLER ET AL. 1988).In pork, pig livers and pig kidneys, as well as beef, and beef liver from Sweden, nickel was found below the detection limit of 0,010 mg.kg -1 wet weight.Most beef kidneys had about 0,014 mg.kg -1 , only a few of them were higher (JORHEM ET AL., 1989).In France, commercially available fish contained just 0,056 mg.kg -1 Ni in wet weight (range 0,032-0,161), and no accumulation was noted in predators.Nickel in other seafood was slightly higher at 0,123 mg.kg -1 (GUÉRIN ET AL. 2011).

International journal of
To simulate corrosion of nickel-plated Cu riflebullets, they were inserted into meat juice for 7 days, and released up to 0,093 mg Ni, which did not result in a significant increase of nickel concentrations around the shot wound of the game meat.Average Ni release of a Niplated bullet during roasting of pork was 0,0028 mg (maximu m 0,0043 mg) (PAULSEN, SAGER 2017).
In whales, higher nickel levels than in domestic animals and fish have been encountered.Nickel in innards from pot whales of the North Sea ranged about 2,5 mg.kg - 1 in dry weight till lower detection limit.The skin of pot whales from 17 non-contaminated areas, sampled as biopsies of obviously healthy free swimming individuals, had 2,4 mg.kg -1 in wet weight.Contrary to this, the skin of finbacks and pot whales from the Gulf of Mexico contained an average nickel of 15,9 mg.kg -1 (range 1,7-94,6 mg.kg -1 ) in 2010, sampled soon after the large oilspill of the drilling platform Deepwater Horizon.All whales looked healthy and had no oil cover at their skin, and moved far from crude oil lumps.Their nickel contents correlated with the distance to the site of the disaster.Because nickel resorption from the gastrointestinal tract is low, and pot whales and finbacks feed on quite different prey, and sorption of the skin seems marginal, the most probable path is the uptake of fine dust to the lungs from the oil combustion during the oil catastrophy (WISE ET AL. 2014).Similar to meat, milk and dairy products are much lower in nickel than green plants (see below).Commercially available cheeses in Austria contained about 0,25 mg.kg -1 in wet weight (SAGER 2012), which was less than Ni in Turkish fresh cheeses at 0,59±0,13 mg.kg -1 wet weight sampled at about the same time.Packing into metal containers additionally increased the nickel level to 1,28±0,08 mg.kg -1 wet weight (BAKIRCIOGLU ET AL. 2011).
The daily pulmonal uptake can be calculated from the concentration (ng.m -3 ) times absorption rate times air breath volume (15-20 m³.d -1 for an adult).The absorption rate in lung tissue had been simulated by use of artificial serum.For the Saloniki region in 1997/98, the daily pulmonal intake in urban areas was thus determined as 56 ng, and in industrial areas as 65 ng (VOUTSA, SAMARA 2002) The oral LD50 amount for rats as 350 mg.kg -1 body weight, and for mice as 420 mg.kg -1 boddy weight, seems rather high.Nickel, however, is teratogenic and exerts a cancerogenic potential, lowering Mg, Mn, and Zn in various tissues (DENKHAUS, SALNIKOW 2002).In the gastro-intestinal tract, usually only 1-2 % get resorbed, the rest gets excreted in the faeces.After incorporation, nickel gets excreted half via urine and half via faeces, the halftime for renal excretion is rather short at 20-60h, but does not exclude deposition in the body (DENKHAUS, SALNIKOW 2002).Quite different reports about resorption and toxicity, however, indicate that the resorption is strongly influenced by simultaneously ingested food, and is maximum for potable water.Different resorption rates resulted in significantly higher blood levels after uptake of 2,5-5,0 mg from potable water or Coca Cola, than from cow milk, orange juice, coffee or tea.Addition of 5 mg Ni to a splendid breakfast did not increase blood nickel levels (SCHELLER ET AL., 1988).In spite of high nickel levels in tea leaves (median 1,70 mg.kg -1 , range 1,2 -2,6 mg.kg -1 ), sampled in entire Asia, nickel remains low in the final beverage because of high adsorption at the leaves (TADAYON, LAHIJI 2011).
Nickel metal and nickel salts can also be solubilized by sweat.The diffusion through the epidermis gets favoured from sweat and detergents and is similar for normal and nickel-sensitive persons.Nickel contact dermatitis develop due to the attempt of the organism to remove nickel-protein complexes, which had been formed in the Langerhans cells in the basal layer of the epidermis (SCHAUMLÖFFEL 2012).

MOLECULAR BIOLOGY
Ni and Co are bound in constant proportions to naturally occurring porphinoid products in some living organisms, which may be due to corresponding functions.nickel can be monovalent and trivalent also, and thus function as a redox substrate in biosystems.Methanogenic bacteria have a methyl-CoM-reductase with a prosthetic group of Ni-porphinoide, where Ni is coordinated with the N of tetrapyrrole (NIELSEN 1991).Ni-deficiency in rats causes changed distribution and function of Ca, Fe, Zn, and vitamine B12 in goats and rats (NIELSEN 1991).In rats during methionine deficiency, nickel acts synergistic to vitamine B12 and effects the concentration of Cu, Fe, and Mo in the plasma, as well as C, Cu and Mo in the liver, and Cu, Mn and Ni in the kidneys (NIELSEN 1991).
Nickel has been identified as an essential nutrient for the activations of urease in green plants (SCHAUMLÖFFEL 2012), or in the bacterium heliobacter pylori (DENKHAUS, SALNIKOW 2002).Nickel at ultratrace levels is needed to fix CO2 to propionyl-CoA, to form D-Methyl-malonyl-CoA. It is a Co-factor of an enzyme to degrade branched amino-acids and oddnumbered fatty acids via the propionate route.The methylmalonyl-CoA, which depends on vitamine B12, catalyses the last step of the propionate metabolism, which increases after increased uptake of odd-numbered fatty acids.The daily need of man is below 100 µg (NIELSEN 1991).
In human serum, the Ni gets preferably bound to albumin, but it also moves to L-histidin and alpha-2macro-globulin (SCHAUMLÖFFEL 2012).Substitution at the albumin also explains the known effects of enhanced excretion of Zn and Cu.Similarly, Ni-intoxication of layers reduces the zinc levels met in eggs (WILPLINGER, PFANNHAUSER 1998).
Nickel causes oxidative damage of the DNA and prevents its repair.It replaces Fe inside the cells an d simulates oxygen deficiency.Carcinogenesis depends from the kind of tissue, nickel speciation, and genetic predisposition.Particulate Ni gets incorporated into living cells by phagocytes, and dissolves there slowly in cytoplasmatic vacuoles at pH 4,5.In human lung cells, after 24h main amounts of incorporated nickel were found in the cytoplasm, but after 72h in the cell nucleus.In the nucleus, substitution of Mg by Ni leads to selective damages at the genetically inactive hetero-chromatine, but Ni per se is not mutagenic.Induction of methylations at the DNA results in switching off of genes because of increased condensation of the heterochromatine.Further on, substitution of Fe by Ni inhibits the hydroxylases of proline and asparagine, resulting in Fe-losses and signalling oxygen depletion inside the cell.This lowers the aerobic metabolism of ATP gains and results in anaerobic glycolysis, as well as to lower levels of acetyl-CoA in the respective cells (COSTA ET AL., 2005).
Patients, who develop genetically based ekzema and heavily itching inflammations of the upper skin because of nickel allergy (table 5), show serious immunological reaction towards membrane blisters of staphylococcus aureus, which penetrate the epidermis.Staphylococcus aureus increases a special messenger substance.Increased water losses and pH increase proliferate staphylococcus aureus in the skin of respective dermatitis patients, counteracted by specific antibiotics and vitamine D (LIMONE, JACOB 2018).
The nickel sensitivity of the skin of 28 nickelsensitive patients could be lowered by fixation of nickelsoaked filterpaper disks during 3 months daily application of 50 µg Ni. a dose which does not develop ekzema.The area of harmed skin was lowered to ½ after an hour, and to 1/3 after 4 days of application.Continuous Ni-release provoked a steady substantial decrease of the reactions of the T-cells with the metal ion to ¼.The number of in vitro tested T-blood cells of the CD4+ and CD8+ type as well as the number of cell partitions got severely reduced.At the end of the treatment, the nickel-stimulated T-cells of patients released less interferon-gamma (BONAMONTE ET AL., 2011).

DAILY INTAKE AND ALLERGICAL REACTIONS
In Great Britain, the daily intake of nickel was estimated from the average concentrations of 20 food groups and the average consumption habits, to be 130 µg.Because data below the detection limit were set as the detection limit, the 130 µg are a maximum value (YSART ET AL., 1999).For Austria, a similar daily intake level of nickel was estimated as 79 µg (range 50-127 µg), but utilizing largely different concentration levels of the ingested nutritional items (WILPLINGER, PFANNHAUSER 1998).Therein, the high nickel levels in carrots and cocoa were confirmed.
The median concentrations of nickel in food found in this work, analytically obtained for wet weight, and combined with the average figures of consumption (Statistik Austria 2012), result in a daily intake of 152 µg Ni.This figure has been calculated without considering consumptions of Ni-carriers like mushrooms, nuts, rice and leafy vegetables, but for wholemeal bread.If consumption of white flour is assumed, the daily Niintake would be just 106 µg, which resembles about the daily needs (Table 6).Wilplinger and Pfannhauser had estimated similar levels for Austria already in 1998.
If consumption of milk is replaced by soy-"milk", and the average consumption of meat replaced by nuts and vegetables of about equal nutritional value, and the proportion of carrots, cabbage and lettuce taken from the harvested amounts in Austria, this results in a daily intake of 496 µg Ni ( It can be shown by ESR-spectra that enzyme-bound International journal of Horticulture, Agriculture and Food science(IJHAF) Vol-3, Issue-2, Mar-Apr, 2019 https://dx.doi.org/10.22161/ijhaf.3.2.6 ISSN: 2456-8635

International journal of Horticulture, Agriculture and Food science(IJHAF) Vol-3, Issue-2, Mar-Apr, 2019 https://dx.doi.org/10.22161/ijhaf.3.2.6 ISSN: 2456-8635 maize
silage, like for most of trace metals, and highest in hay.The lucerne sample (table 2) was used for a round robin test, which had to be ground and milled in 24 different laboratories, and subsequently analyzed at the same site by the same operators and instruments, after dry-ashing of 4g (SAGER, MITTENDORFER 1997).The latter should indicate the precision of the entire analytical procedure.

Table 3A .
Nickel in food of green plant origin, mg.kg -1 dry mass

Table 7 )
. In this case, Ni-sensitive persons

International journal of Horticulture, Agriculture and Food science(IJHAF) Vol-3, Issue-2, Mar-Apr, 2019 https://dx.doi.org/10.22161/ijhaf.3.2.6 ISSN: 2456-8635 begin
to react, and at the double amount of ingestion, about 10-30% will react (Table7).Nickel allergic persons develop contact ekzema after oral ingestion of a few milligrams, an amount which can be easily reached by consumption of nuts, cocoa or soy drinks (JENSEN ET AL.2006).17 papers dealing with the probability of an onset of Ni-dermatitis could be assigned to 3 groups, depending on the kind of uptakefrom water or solid food, on the visible symptoms and on the observation period (JENSEN ET AL. 2006).

Table 6 :
Estimation of Ni-ingestion from the average food consumption (2011/12): without rice, mushrooms, nuts and leafy vegetables, but with wholemeal flour If the figure for German standard bread is taken instead (0,069 mg.kg -1 ; BRÜGGEMANN, KUMPULAINEN 1995) the daily intake is lowered to 106 µg; eggs contained nickel below detection limit, and need not to be considered

Table 7 :
Estimation of Ni-ingestion from the estimated average food consumption for vegans, substituting milk by soy -"milk" and meat by vegetables and nuts (2011/12):