Heavy Metal Built-Up in Agricultural Soils of Pakistan: Sources, Ecological Consequences, and Possible Remediation Measures

Abstract

Pakistan is an agricultural country with two thirds of the population depending on the agriculture sector for their livelihood. The increasing population growth rate (1.49 %) has placed an immense pressure on resources and continuous food/fiber demands from varying agroecological zones of the country. Increased agricultural production has compromised soil ecosystems in specific and agricultural environments in general. Farmers have adopted all means, i.e., agricultural mechanization, usage of pesticides, increased fertilizer use, wastewater irrigation, application of municipal and industrial solid wastes/sludges/composts, and monoculture to increase agricultural production. In response to all such anthropogenic activities, soil fertility and health are continuously on decline. Soils act as sink to all anthropogenic activities and substances either organic or inorganic, i.e., heavy metals. Ways and means employed to enhance agricultural productivity continuously add heavy metals into soil ecosystems which are extremely cytotoxic, teratogenic, carcinogenic, and mutagenic. Atmospheric deposition and vehicular emissions are also adding heavy metals to the agricultural soils. Food chain contamination is the ultimate result of increased metal levels in soils which are biomagnified in the food crops and fodder. Heavy metal contamination of food crops leads to serious health concerns in the consumers, i.e., humans and livestock. Various researchers have highlighted elevated metal levels in the agricultural soils from different agroecologies of Pakistan presenting the current status, biomagnification, and related potential ecological health problems. Chemometric and GIS approaches in this regard have been successfully employed to understand the origin, relationship, and spatial distribution patterns of heavy metals in the contaminated agricultural soils. In current review of heavy metal contamination in agricultural soils, several remediation techniques, i.e., mycoremediation, phytoremediation, and bacterial bioremediation, have also been reported from Pakistan to offer an economic, environment-friendly, and viable solution to reclaim contaminated soils. All three bioremediation types employed by different researchers in Pakistan befit the country’s energy and climatic conditions. Through genetic engineering abilities of plants, fungi and bacteria can be enhanced to attain the desired bioremediation results in polluted environments either in situ or ex situ. Good agricultural practices and reduced chemical input can slow down further heavy metal built-up in soils.