Chapter 7
Trace Metal Content of Commercial Fertilizers Marketed in Lebanon
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Isam Bashour, Ghada Hannoush, and Nasri Kawar Faculty of Agriculture and Food Sciences, American University of Beirut, Beirut, Lebanon
Recently, concern has been expressed over trace metals that enter the food chain. Inorganic fertilizers are considered among the potential sources of contamination. The majority of fertilizers marketed in Lebanon are imported from Europe and Middle Eastern countries. A total of 67 fertilizers samples were analyzed for Cd, Co, Cr, Ni, and Pb. Results show that most fertilizers contained low concentrations of these trace metals, but there is considerable variation in metal concentration detected among the samples. Highest concentrations of trace metals were found in granular phosphate sources followed by liquid formulations. Lowest concentrations of metals were found in soluble crystalline fertilizers. In general, the metal concentrations for Cd, Co, Cr. Ni and Pb were in the low in comparison to the range of values reported internationally for fertilizers.
Introduction Inorganic fertilizers are used at high rates by Lebanese farmers in order to increase crop yields. Currently there are no regulations for fertilizer application rates or maximum concentrations of trace metals in fertilizers marketed in Lebanon. The concern of the public is increasing regarding the possibility of soil, water and food contamination with trace metals from excessive and repeated use of commercial fertilizers. Schroeder and Balassa (1963) noted that repeated fertilizer applications may raise the concentrations of some trace metals in food such as C d that can be taken readily by plants and enter the food chain. Allay (1971) and Kpomblekou and Tabatabai (1994) reported that the main source of fertilizer-derived trace metals in soils is phosphatic fertilizers manufactured from rock phosphate deposits. Soils naturally contain quantities of trace metals, due to weathering of the underlying parent material but
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© 2004 American Chemical Society In Environmental Impact of Fertilizer on Soil and Water; Hall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2003.
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91 additional accumulation may occur from sources like mineral fertilizers, manure and industrial activities. Many trace metals are not essential for plant growth, but can be absorbed by plants, to pass into the food chain and may cause health problems whenever they are present in high concentrations Oliver (1997). Swaine (1962) compiled a comprehensive report about trace element content of fertilizers in the world and showed that all fertilizers contain trace metals but in varying amounts. Charter et al, (1993) showed that Ρ fertilizers such as triple super phosphate, diammonium phosphate and monoammonium phosphate contained variable concentrations of many trace metals. Fertilizers in the Lebanese market are about 25% produced locally and about 75% imported from Europe and Middle Eastern Countries. No information is available about the concentration of trace metals in fertilizers marketed in Lebanon. This work was initiated to assess the content of specific trace metals Co, Cr, Cd, N i and Pb in most of the fertilizer materials marketed in Lebanon. With this information it will be possible to begin to evaluate the risk of potential accumulation of these metals in Lebanese soils.
Materials and Methods Between 1998 and 2000, 67 fertilizer samples were collected from fertilizers marketed in Lebanon. Samples were divided into 4 groups according to their nutrient content: N-fertilizers (12 samples); P- fertilizers (21 samples), K-fertilizers (9 samples) and N P K blends (25 samples). The samples were analyzed for their contents of Cd, Co, Cr, N i and Pb according to the methods of analysis of the Association of Official Analytical Chemists (Williams, 2000). A sample of 1.0g was dissolved in 5 m L concentrated HC1 in a 25 m L beaker covered with watch glass, boiled for 10 minutes and then evaporated to near dryness. After cooling, the contents were boiled with 10 ml 0.1 M HC1 and quantitatively transferred into a 25 m L volumetric flask after filtration through Whatman no. 42 filter paper. The filtrate was analyzed for Cd, Cr, Co, N i and Pb using G B C 902 atomic absorption spectrophotometer.
Results and Discussion Concentrations of Cd, Cr, Co, N i and Pb in the samples are presented in Tables I-III. The data indicated that concentrations of trace metals are highest in granular phosphatic fertilizers (SSP, TSP, D A P and M A P ) followed by liquid phosphatic fertilizers. The water-soluble powder fertilizers, N-fertilizers and K fertilizers generally contain relatively low concentrations of trace metals. N-Fertilizers The major sources of Ν fertilizers in the Lebanese market are ammonium sulfate (21%N), ammonium nitrate (33.5%N) and urea (46%N). Results of the analyses are presented in Table I & Figure 1 and show that the three Ν sources
In Environmental Impact of Fertilizer on Soil and Water; Hall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2003.
92 are relatively free of Cr and Co. Ammonium sulfate and ammonium nitrate did contain measurable amounts of Cd, N i and Pb ranging between 1.5 - 7.2 mg C d Kg" ,
