**4.3 Industrial waste**

It is estimated that 20 million hectares of agricultural land are irrigated with wastewater from industry or households. In several cities in Asia and Africa, studies show that agriculture based on wastewater irrigation accounts for 50% of the vegetable supply to urban areas. Farmers are less concerned about environmental benefits or harms, maximizing yields and profits. Even though the concentration of heavy metals in wastewater is relatively low, long-term irrigation can lead to its accumulation in the soil [53]. In Indonesia, heavy metal pollution has been identified in watersheds. According to [54], paddy soils in the Solo downstream watershed have been contaminated with Pb. Furthermore, paper mill effluent irrigation water has polluted the soil with Cu, Pb, and Cd. The Juwana sub-watershed indicates that heavy metal Cr contamination has the potential to contaminate agricultural land because the irrigation uses sugar industry waste. **Table 5** shows the industrial type producing some heavy metals.


### **Table 5.**

*Types of industries whose raw materials produce heavy metals [55].*
