Concentration of Fe (mg/kg) in soil amended with different treatments of MSW
The results of Year 1 (Y1) showed the minimum Fe concentration at Control in C. vulgaris (Figure 1) and the maximum was observed during Year (Y2) at Treatment (T3) in M. arvensis. The concentration of Fe varied significantly in A. esculentus during Year 1 and in A. esculentus during Year 2 (Table 1).
Iron is a crucial soil nutrient essential for optimal plant growth; however, elevated levels of iron in the soil can potentially hinder the growth of plants due to its toxic effects (Zaheer et al., 2020). The concentration of Fe in the soil of all vegetables was below the standard limits of 150 mg/kg set by WHO, 2000. Iron contents in the present investigation were found to be higher in T3 soils than the maximum permissible limit (56.90 mgkg-1) given by Dosumu et al. (2005). Tasrina et al. (2015) reported a high Fe level in contaminated soil as compared to current findings. Adjia et al. (2008) observed a high Fe level in amended soil (391-1299 mg/kg) were above the permissible limit of 425.11 mg/kg reported by FAO/WHO, (2001). Inoti et al. (2012) observed exceeded concentration of Fe in soils of contaminated sites. In another study, it was reported that domestic and manufacturing units release Fe into the environment (Makuleke & Ngole-Jeme, 2020) (Table 2).
Concentration of Fe in vegetables grown in soil amended with different treatments of MSW
In vegetables, concentration of Fe in A. cepa at Y1 and in L. acutangula at Y2 differed significantly (Figure 2). Lokeshappa et al. (2012) also reported similar results in different vegetables. The concentrations of Fe were below the permissible limit recommended by WHO, (1996). The concentrations of Fe in vegetables recorded in the present study were lower than the reference values cited by Chiroma et al. (2014). Fe is a fundamental component for living organisms and involved in photosynthesis as it is crucial for the production of chlorophyll in plants. It is also essential for the proper functioning of many catalysts. Excessive exposure to iron in vegetables for human consumption leads to several health issues, including renal, neurological system, and bone illnesses (Steenland & Boffetta, 2000). Fe also takes part in the formation of hemoglobin in higher animals (Nawab et al., 2016). The value of Fe was recorded <500 mg/kg lies in dangerous limit (Kabata-Pendias, 2011). Fe concentration was similar to a previous study conducted by Zahir et al. (2009) in different vegetables collected from local markets of Pakistan. In plants, iron toxicity develops when the amount of iron in the soil falls below 300 mg kg-1 and the pH falls below 5.0 (Yu et al., 2006). Inoti et al. (2012) observed exceeded concentration of Fe in vegetables grown indifferent contaminated sites.
Concentration of Fe in the serum of human
Results of variance analysis presented that the site was significantly affecting metal concentration in human blood. Order of metal concentration was detected as S0<S1<S2<S3 (Figure 3). A higher level of Fe was observed at S3 while the lowest concentration was detected in S0. Iron is essential as well toxic metals and Wilson’s infection, and hemochromatosis are reported due to Fe toxicity (Brewer, 2010). Health implication for Fe concentration in human blood include anemia, infectious and inflammatory diseases, blood loss from parasitic infections, and other nutrient deficiencies (Brabin et al., 2001). The connection between higher blood lead concentration and Fe insufficiency was assumed by Muwakkit et al. (2008) and Hegazy et al. (2010a) (Table 3).
PLI was used to find the contamination level of the location (Adebowale et al., 2009). The low value of PLI was observed at Control during Y1 in the soil of C. vulgaris and a high was found at T3Y2 in M. arvensis (Figure 4).
PLI values greater than 1 are considered as contaminated, whereas PLI values lower than 1 as uncontaminated (Harikumar et al., 2009). Low contents of PLI were exhibited by Rahman et al. (2012) in the contaminated site of Bangladesh. Value of PLI exceeded 1 which suggested that application of MSW significantly affected the concentration of metals into the soil and in turn into the grown vegetables (Chary et al., 2008).
The range of PLI was 1.212-1.42. In this investigation, the PLI results for Fe were less than the Fe reference values (56.90) reported by Dosumu et al. (2005). El-Anwar (2019) observed a high PLI value as compared to current results (PLI 2.6). High PLI was due to different factors including industrial activities, agricultural runoff and several man-made activities (Uwah et al., 2009). The high value of PI was found during the current study as compared to the results of PLI (0.557- 0.726) as observed by Malik et al. (2019) in the MSW amended soil. Singh et al. (2010) also recorded higher metal pollution index in Momordica charantia L., so the consumption of such vegetables with high iron accumulation may cause hazardous effects in humans (Table 4).
Bio concentration factor (BCF) of the Fe
The value of BCF ranged from 0.1671 to 0.713. The higher BCF was observed at T3 during Year_2 and lower BCF at Control during Year_1. The minimum value was noted in S. melongena (Figure 5). It was observed that L. acutangula showed higher BCF at all amendment treatment (T1, T2, T3) might be due to municipal solid waste amendment.
Metal uptake by plants is affected by a number of factors such as soil pH, soil metal levels, soil organic matter content, soil cation exchange capacity, plant age, and types and crop varieties (Barančíková et al., 2004). The metal value into the plants was found higher than in the soil as indicated by high value of BCF by 1 (Murray et al., 2011). All BCF values for Fe were below 1.0, indicating that the metal did not bioaccumulate in the vegetables. The capacity to absorb and transfer metal within the plant differs from species to species (Vasiliadou & Dordas, 2009). Current results were following Murray et al. (2011) who found low BF values for vegetables grown in MSW amended urban garden soils. The bioavailability of metals differs from plant to plant and different plants showed different capacities to uptake a metal (Singh et al., 2010) (Table 5).
Enrichment factor (EF) of Fe
EF was ranged from 0.022345-0.095384. Highest EF was noted in the soil of L. acutangula at T2Y2. While minimum EF was observed in the soil of S. melongena at Control during Y1 (Figure 6). EF showed low enrichment of metal, however overall comparison between treatments showed higher EF at T3 (75%) MSW amendment and lower EF at control with no amendment. Current EF contents were lower than Likuku et al. (2013).
Lower EF was observed by Khan et al. (2020b) than current values. Present reported EF value was lower than Nayak et al. (2015) who reported high enrichment of Fe. Our EF value was lower than Balkhair and Ashraf (2016) and Nour et al. (2021).
In contrast to current findings, Sarwar et al. (2020) observed a higher value of EF (386) for iron metal. Ahmad et al. (2018) reported a higher value of EF (0.134) as compared to present findings. Kumar and Chopra, (2012) described EF of Fe which was comparable to the current value. The present observed EF was less than 1 while in the previous study by Chauhan, (2014) EF was greater than 1. EF <2 showed minimal enrichment of metal (Alghobar & Suresha, 2015). The EF value in our study was less than the EF value given by Chabukdhara et al. (2016). The present investigated EF value was less than 1, suggesting that the site was not highly enriched with iron (Table 6).
Health Risk Index of Fe
Maximum DIM was recorded in L. acutangula at T3Y2 and minimum was in S. melongena at Control during Y1 (Figure 7). The DIM was from 0.00566 to 0.027761 mg/kg/day. Health risk index of Fe was higher in L. acutangula at T3Y2 which was (0.039659) while lower HRI was observed in S. melongena which was (0.008085) (Figure 8).
Provisional tolerable daily intake of vegetables is 117g/day helps in the estimation of health risk assessment (Khan et al., 2009). DIM determined the level of toxicity in humans. In the current findings, the highest value of DIM was found in L. acutangula at the contaminated site but this concentration is free of risk and safe for consumption by human beings because the dietary intake limits of Fe are 10.0 to 50.0 mg (WHO, 1996). The iron (Fe) intake in all the samples remained below the daily permissible limit of 45 mg/kg/day as suggested by USEPA (2002). Gebreyohannes and Gebrekidan (2018) recorded DIM content (0.083) which was higher than the present investigated DIM content. Latif et al. (2018) reported higher DIM content in vegetables when compared to the present findings. Current DIM values for Fe were much lower as compared to values reported by reported by Harmanescu et al. (2011).
Comparable results with the present findings were recorded by Mezgebe et al. (2015). Harmful effects of heavy metals via ingestion of food plants on human beings could be determined by the risk assessment index. HRI value lower than 1 showed lower associated risk (Akoto et al., 2014). Our findings were lower than the tolerable value given by FAO/WHO (1999a). Khan et al. (2017) discovered a comparable range of HRI (0.01, 0.02) for Fe as compared to current findings. HRI value of all the studied vegetables was observed less than 1 which indicated that there was the comparative nonappearance of health hazards accompanying the consumption of polluted vegetables growing in sewage-contaminated sites. The findings were in accordance with the results of Khan et al. (2008a) (Table 7).