Heavy Metals in Surface Soils and Crops

*Mohammad Velayatzadeh*

### **Abstract**

In the era of industrialization and technological progress, pollution has reduced the quality of life for humans. Heavy metal pollution is one of the main causes of environmental degradation. The underlying causes are natural as well as human. Heavy metal contamination of soil has become a worldwide environmental issue that has attracted considerable public attention, mainly due to increased concern for the safety of agricultural products. Heavy metals refer to some metals and metals with biological toxicity such as cadmium, mercury, arsenic, lead and chromium. These elements enter the soil agricultural ecosystem through natural processes resulting from raw materials and through human activities. Heavy metal pollution is a great threat to the health and well-being of animals and humans due to the risk of potential accumulation through the food chain. The main sources of heavy metal pollution are air pollution, river sediments, sewage sludge and municipal waste compost, agricultural chemicals such as fertilizers and pesticides, and industrial wastes such as factories that release chemicals. Heavy metals can enter the water supply through industrial and consumer wastes or even from acid rain that decomposes soils and releases heavy metals into streams, lakes, rivers and groundwater.

**Keywords:** soil pollution, heavy metals, toxic elements, human health, crops

### **1. Introduction**

The progress of industries and the growth of urban communities have caused an increase in man-made pollution caused by industrial and agricultural activities and many pollutants enter the environment [1]. One of the most important pollutants in the environment is soil pollution [2]. Soil pollution includes the entry of physical, biological, and chemical substances into this environment, which will eventually enter the life cycle of animals, plants, and as a result, humans, and will cause negative effects in the life of living organisms [3]. One of the effects of soil pollution is the reduction of plant growth and development, which causes the loss of vegetation and ultimately leads to soil erosion and desertification [4]. Most of the pollution created in the soil is caused by the discharge or leakage of organic substances. Petroleum substances and their derivatives cause soil pollution as a result of transportation or storage, while the deeper the petroleum substances penetrate into the soil, the more difficult it is to remove the pollution and the cost will be several times higher [5].

Soil pollution is very dangerous and due to the fact that this type of pollution, like air and water pollution is not directly related to human life, less attention has been paid to it. Soil is one of the valuable resources of nature, which provides about 96% of the food needed by humans [6]. Healthy and clean soil is very necessary and important for life on earth. Day by day, soil ecosystems become a place for harmful substances, scum, waste, and receiving harmful substances, and more than the weather, their pollution burden increases, and on the other hand, more and more Due to the construction of buildings, roads and urban and industrial facilities, a large amount of soil is taken out of the natural circulation and also from the agricultural area and becomes dead soil. Therefore, proper management to have a healthy soil is necessary for human survival [7]. Soils have a special advantage called self-purification and they are considered to be nature's purifiers, but the self-purification power of soil is less than the self-purification power of water and air due to its low exchange with other regions and areas, for this reason soil pollution, It is considered one of the most important types of environmental pollution [8].

Heavy metals are a group of metals and quasi-metals, whose amounts and concentrations are toxic and dangerous. Mercury, lead, cadmium and arsenic can be mentioned from the group of toxic metals [9]. Because heavy metals enter the soil through anthropogenic activities or exist naturally in the soil texture, they can easily and very quickly cause soil pollution [10]. In addition to directly affecting the physical and chemical properties of the soil, reducing biological activity and reducing the bioavailability of soil nutrients, heavy metal pollution is also a serious threat to human health through entering the food chain and environmental security through penetration into They are considered underground waters [11].
