Nickel speciation in soil and the relationship with its concentration in fruits

Interest in the potential link between cancer and some inorganic nickel com pounds (Nriago 1980) has drawn attention to the Ni concentration in food an d other environmental samples. The studies of the uptake and chemical behav ior of Ni in plants are related mainly to its toxicity having possible impl ications with respect to animals and man. On the basis of a report publishe d by the International Committee on Nickel Carcinogenesis in Man (ICNCM) (R eport 1990), the International Agency for Research into Cancer concluded th at (i) there is sufficient evidence to establish a correlation between nick el sulfate and combinations of nickel sulfides and oxides and the incidence of lung and nasal cancers; (ii) there is inadequate evidence to establish a similar correlation for metallic nickel and nickel alloys; and (iii) limi ted evidence in experimental animals for the carcinogenicity of Ni compound s including metallic nickel, alloys and various nickel salts. The anthropog enic nickel sources of soil are the metal processing operations and the com bustion of coal and oil because organic matter reveals a strong ability to absorb Ni; so, this metal is likely to be concentrated in coal and oil. In particular, nickel in sewage sludge that is present mainly in organic chela ted forms is readily available to plants and therefore may be highly phytot oxic. The general approach for the soil speciation studies has been to separate t he soil into different chemical reagent or solvent fractions and, by analyz ing each fraction, to determine the amount of element combined or associate d with each soil fraction or phase (Ure 1991). A number of extractants, inc luding ethylenediaminetetraacetic acid (EDTA), diethylenetriamine pentaacet ic acid (DTPA), acetic acid, ammonium acetate, calcium chloride and hydroxy lamine hydrochloride have been tested to identify metal species as exchange able, carbonate-bound, Fe and Mn oxide-bound, organically bound, and to est imate the plant available trace metals. Flame atomic absorption spectrophot ometry (FAAS) has proved to be a reliable, convenient and rapid method for analysis of toxic and nutritional metals in food, biological and environmen tal matrices, as direct or, particularly, in combination with preconcentrat ion method (Morales et.al. 1993; Gucer and Yaman 1992; Yaman and Gucer 1994 , 1995a, 1995b and 1998; Yaman 1997, 1998 and 1999; Alegria et. al. 1988). In this study, nickel concentrations in the fruit samples were determined b y FAAS after preconcentration on activated carbon. Soil samples were dissol ved by using the extractants such as the mixture of nitric acid/hydrogen pe roxide, oxalic acid, Na(2)EDTA, acetic acid and citric acid and the extract s were analyzed for Ni by using direct FAAS measurements. So, the relation between the fruit nickel contents and the soil extractants-Ni contents was investigated. In addition, the possible chemical forms of Ni in soil were e valuated.