The management of municipal solid waste is becoming the major challenges in urban community in many developing countries (Karak et al., 2012; Menikpura et al., 2013). The solid waste collection rate is the lowest and even the collected solid waste is disposed to open landfills. The organic component of the urban waste is about 45–60 % the total solid waste generated in developing countries (Pattnaik & Reddy, 2009). Improper management of biodegradable organic waste releases greenhouse gases such as carbondioxide and methane in the environment due to anaerobic digestion from open disposal sites which affects climate change. So, that a sustainable solid waste management scheme is required for the exponential increasing of municipal solid waste generations.
Municipal solid waste application to arable land is a sustainable practice of both soil fertility and waste management. Several studies have showed that MSW compost is common practice to improve the physical, chemical and biological properties of impoverished soils by supplying organic matter (Habib et al., 2015; Haghighi et al., 2016; Srivastava et al., 2016, 2018; Weerasinghe & De, 2017). The organic part of municipal solid wastes is recognized as important source soil organic matter, which can provide essential soil nutrients (Ayilara et al., 2020; Lucchini et al., 2014).
However, a heavy metal contamination is the main challenge to use MSW for agricultural use. MSW could be contaminated by heavy metals from many sources such as house hold dust, electronics, plastics, paints and inks and pesticide (Chimuka & Manungufala, 2009). All types of municipal solid waste (MSW) compost contain more heavy metals than the background concentrations present in soil and will increase their contents in amended soil and the heavy metal transfer into plants (Smith, 2009). Studies have showed that compost amended soils had increased significantly in the contents of Cd, Cr, Cu, Ni, Pb and Zn compared to untreated soils (Ayari, 2010; Carbonell et al., 2011). Consequently, there is evidence of phytotoxic effects, or accumulations of heavy metals in crop tissues that may pose a risk of human health from the applications of MSW compost to the soil (Basta et al., 2004; Paradelo et al., 2020; J. Singh & Kalamdhad, 2011).
High levels of heavy metals in soil, water and food supply adversely affects food chain, human health and soil ecosystems. Therefore, consumption of heavy metal contaminated foods is the major route of human health risk (Guerra et al., 2012; Mahfooz et al., 2020). Heavy metals are non-biodegradable and persistent in the environment, which are known to cause toxic effects on animal and human health. Once they enter into our body, they are converted into more dangerous organic forms and accumulate in fatty organs such as liver, kidney and skin. Organic forms of heavy metals are water insoluble which is difficult to eliminate from our body and damage these organs. Thus, heavy metals especially, lead (Pb), cadmium (Cd), and Chromium (Cr) are the most toxic and affect human health even at low concentration (Khan et al., 2008; Qureshi et al., 2016; Shaheen et al., 2016; Volpe et al., 2009; Wassim et al., 2018). As heavy metals can play a role in the development of carcinogenic and non- carcinogenic diseases (Wassim et al., 2018a), a decreased in mental capacity, kidney damage, blood and bone disorders, and neurological damage are caused from exposure of heavy metals (Li et al., 2015).
Many research works were done to investigate the bioavailability and human health risk of heavy metals in soil amended with sewage sludge (Pascual et al., 2004; Singh & Agrawal, 2008), soils and vegetables around waste incinerators (Li et al., 2015), and vegetables grow on soil irrigated with wastewater (Hossain et al., 2015; Mahfooz et al., 2020; Qureshi et al., 2016; Sharma et al., 2016; Woldetsadik et al., 2017). There were also research works on risk assessment of heavy metal on soil treated with organic waste compost (Chaney, 2018; Jiwan & Kalamdhad, 2014; Soobhany et al., 2015). But, there is limited study focusing on risk assessments of heavy metals in plants grown on soil amended with municipal solid waste compost. Bioavailability of heavy metals in the edible portion of each crops varied significantly according to the type of crops (Chen et al., 2014; Edogbo et al., 2020). Leguminous vegetables were more likely to accumulate Cr, while leaf vegetables tended to show higher levels of concentration of Cd and Pb (Chen et al., 2014). Before large scale agricultural applications of organic fertilizers derived from municipal solid waste, data on accumulation and health risk of heavy metals is very important. So, the applications of all organic wastes to arable land must be regulated with regard to tolerable amounts of nutrients and heavy metals (Seçer et al., 2016). Thus, the aim of this study was to assess the bioavailability and health risk of faba bean grow on soil amended with compost, khat biochar and co-composted biochars derived from municipal solid waste.