**4. Sources and causes of Pb and Cd pollution in agriculture**

### **4.1 Phosphate fertilizer**

P fertilizer is regularly applied to the soil in intensive farming systems to increase plant growth. The compounds used contain heavy metals Pb and Cd [14, 40]. Triple super phosphate (TSP) fertilizer supplied excessively in rice fields in the long term will be accumulated and cause pollution because of heavy metals. These metals are also present in natural phosphate rock used as the raw material for the manufacture of fertilizer P [14, 41]. Pb and Cd are known to have no physiological activity/function, and applying certain phosphate fertilizers adds Cd and other potentially toxic elements to the soil, such as F, Hg, and Pb [42]. Phosphate fertilizers can significantly contribute to hazardous trace elements such as arsenic (As), Cd, and Pb in croplands. These trace elements have the potential to accumulate in soils and be transferred through the food chain [11]. Various inorganic fertilizers and those derived from phosphate rock contain heavy metals (**Table 4**). The results of different phosphate fertilizers showed the presence of P2O5; secondary Ca and Mg; microelements Fe, Mn, Cu, and Zn; and heavy metals Cd, Cr, Pb, Cu, and Hg in varying amounts, namely, Cd (0.1–170 mg kg−1), Cr (66–245 mg kg−1), Pb (40–2000 mg kg−1), and Cu

*Heavy Metals in Indonesian Paddy Soils DOI: http://dx.doi.org/10.5772/intechopen.109027*


### **Table 4.**

*Heavy metals in various types of natural phosphate rock and SP-36 [43].*

(1–300 mg kg−1) [44]. Long-term P fertilizer applications are likely sources of heavy metals (Pb and Cd) in agricultural soils and crops [45, 46].

From the analysis of P fertilizer, TSP fertilizer contains 120.60 Pb mg kg−1 and 4.90 mg kg−1 Cd, while single superphosphate (SP)-36 contains 5.3 mg kg−1 Pb and 10.43 mg kg−1 Cd. Rai et al. [47] explained that using P fertilizer could cause the soil accumulation of Pb and Cd. Furthermore, it contains heavy metals Pb and Cd from the raw material for making P fertilizer. Natural phosphate rock has various associated elements such as Pb and Cd in high enough quantities. Meanwhile, the elements can be dissolved in soil solution, adsorbed by organic and inorganic colloidal surfaces, firmly bound in soil minerals, deposited by compounds in the soil, and contained in living materials.

### **4.2 Pesticide**

Generally, pesticides are widely used in agriculture and horticulture, containing heavy metals. For example, about 10% of pesticides in England contain compounds of Cu, Hg, Mn, or Zn. Fungicides are pesticides containing Cu, such as a mixture of Bordeaux (copper sulfate) and copper oxychloride. Lead arsenate has been used in orchards for many years to control several parasitic insects. Arsenic-containing compounds are also extensively used to control cow lice and banana pests in New Zealand and Australia. Wood preservation using formulations of Cu, Cr, and As pollute the air due to excessive concentrations of heavy metals [27, 48]. In Indonesia, the use of pesticides on vegetable crops is very intensive, especially on cash crops with high economic value. Based on research, 30–50% of the total production cost is used for pesticides [49]. Intensive use can increase soil and plant residues and even enter the bodies of animals, fish, or other aquatic biotas. Pesticides with a long half-life of degradation can harm the health of humans that consume products containing these residues.

Organic waste (biosolid) is a solid product produced through a wastewater treatment process and can be recycled. In the United States, it is estimated that more than 50% of the approximately 5.6 million tons of dry waste is used or distributed annually on land. Biosolids are applied to agricultural land in every region of the state. In European society, more than 30% of this waste is used as fertilizer. In Australia, 175,000 tons of dry biosolids are produced annually by

local governments. Other biosolid materials are sawdust, rice/corn straw, or plant residues [50]. Heavy metal contamination of the soil may result from the continued application of biosolids. The most common heavy metals found in biosolids are Pb, Ni, Cd, Cr, Cu, and Zn, and the concentration depends on the intensity of industrial activity [51]. The application can be leached into the soil profile and potentially contaminate groundwater. It was shown that continued application of biosolid to several soils in New Zealand resulted in increased concentrations of Cd, Ni, and Zn in drainage water [52].
