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The In�uence of Compost Amendments on Bioaccumulation of PotentiallyToxic Elements by Pea Plant Cultivated in Mine Degraded SoilsMuhammad Irfan 

College of Engineering Najran UniversityMuhammad Azhar Shah 

Department of Horticulture, The Agriculture University PeshawarMehboob Alam 

Department of Horticulture, the Agriculture University PeshawarAnwarzeb Khan  ( khan.anwarzeb@yahoo.com )

University of SwatMuhammad Amjad Khan 

University of PeshawarSaifur Rahman 

College of Engineering, Najran University, Saudi ArabiaMabkhoot A Alsaiari 

College of Engineering, Najran UniversityMohammed Saeed Jalalah 

College of Engineering, Najran UniversityMohammad Kamal Asif Khan 

College of Engineering, Najran UniversityAbdulnour Ali Jazem Ghanim 

College of Engineering, Najran University

Research Article

Keywords: PTEs, Compost, Organic matter, Mining soils, Pea, Human health

Posted Date: September 11th, 2021

DOI: https://doi.org/10.21203/rs.3.rs-880760/v1

License: This work is licensed under a Creative Commons Attribution 4.0 International License.   Read Full License

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AbstractPotential toxic metals (PTEs) accumulation in soil and water is one of the major sources of food crop contamination. PTEs remediation from soil can beenhanced by addition of organic matter to the growing media. An experiment was carried out to investigate the effect of different organic amendments on theaccumulation of PTEs in pea plant grown on mine degraded soils. Mining soils from chromite mine (CM), soap stone mine (SSM), manganese mine (MM) and quartz mine (QM) were mixed with vermicompost (VC), leaf mould (LC) and spent mushroom compost (SMC) along with garden soil at 1:1:1 ratio.Various growth and yield related attributes of pea plant as well as PTEs concentrations in soil and plants were studied. The highest Cd (2.62 mg kg−1) and Cr(13.6 mg kg−1) concentration was reported in CM soil, while Pb (23.3 mg kg−1) and Mn (59.2 mg kg−1) concentration in SSM and MM soil, respectively. Miningsoils signi�cantly reduced the plant growth and yield, while organic amendments reduced the PTEs availability and increased pea plant growth. Comparingthe various organic fertilizers used, it was observed that VC e�ciently reduced Cd, Cr, Pb and Mn uptake by pea plant, subsequently, improved pea plantgrowth. In order to assess the effects of various amendments on PTEs health risk reduction various risk indices including, plant trafser factor, average dailyintake, health risk, target hazard quotient and target cancer risk were also calculated and the results revealed that application of compost particularly VCsigni�cantly reduced the dietary intake and health risks of PTEs. 

IntroductionMining activities disturb the surrounding environement badly and the toxic metals secretion from them negetatively affect soil and water (Nouri et al. 2009).Toxic metals from minning can reach the soil mainly through water and subsequently contaminate edible crops. They can affect soil environment for longerperiod of time due to their non-degradable properties and longer half lives. Plants can absorb many different elements from soil, while some of them areessential for plants, others are non-essential and accumulate in various plant parts. PTEs may include plants essential (Copper (Cu), Manganese (Mn), andZinc (Zn)) and non-essential (Cadmium (Cd), Manganese (Mn), Lead (Pb), Chromium (Cr), etc.) elements. Growing plants on toxic metals polluted soils mayaffect the plants metabolism and biochemical processes, which results in restricted growth, poorer biomass production and metal accumulation (Khan et al.2015a,b; Alam et al. 2020). One of the common consequences of PTEs toxicity is the formation of metal complex within the plant cell, after beingaccumulated (Kalaivanan and Ganeshamurthy 2016). Simialrly, toxic metals accumulation can lead to the formation of reactive oxygen species (ROS), whichcan cause inactivation of enzymes, DNA damage and its interaction with other vital plant cell constituents (Pourrut et al. 2013). Likewise, a large number ofphysiological and biochemical processes in plants are also negetaively affected by metal toxicities. Toxic metals once absorbed by the plants can interferewith physiological activities including but not limited to photosynthesis, gaseous exchange and nutrient absorption, consequently causes reductions in plantgrowth and yield (Khan et al. 2016). They may also interfere with the levels of antioxidants, and reduce the nutritive value of the plants (Khan et al. 2015b;Sharma and Agrawal 2005).

Human, upon the consumption of toxic metals contaminated crops, can aquire chronic diseases including cancer, kidneys damage, cardiovascular diseases,gastrointestinal infections, neurological and psychological issues, such as tremor, restlessness, anxiety, sleep disturbance and depression (Mebrahtu andZerabruk 2011; Muller and Anke 1994). Similarly, consumption of food containing toxic metals can signi�cantly reduce the essential nutrients in the body andcauses gastro intestinal cancer (Oliver 1997).

Normally, toxic metals are persistent in nature and accumulate in soil, water and plants for longer periods (Paz-Ferreiro et al. 2014; Chehregani et al. 2005).Therefore, their removal through eco-friendly techniques is utmost important. In this context mixing organic matter to the contaminated soils can play a vitalrole. Essentially, the goal of any remediation experiment based on soil amendments should be to achieve maximum reduction in the bioavailability of PTEs byimmobilization in soil. Various organic and inorganic amendments have been practiced in order to remediate or immobilize toxic metals from contaminatedsoils including municipal and bio solid composts, farm yard manures, sewage sludge, bark chips, woodchips, vermicompost, lime, charcoal, �y ash andbiochar, etc. (Clemente et al. 2007; Somerville et al. 2018; Buema et al. 2020; Khan et al. 2020; Rozek et al. 2021). Soil amendments reduce metals toxicity bythrough metal immobilization that may ultimately affect their bioaccumulation in cultivated. Organic amendment enhances the binding capacity of toxicmetals, improves the availability of soil organic material and reduces their mobility in the soil (Liu et al. 2007). Similarly, organic fertilizers have the ability toreduce phyto toxicity and bioavailability of PTEs in soil. Studies have shown that these organic fertilizers can signi�cantly reduce the concentrations of toxicPTEs in soil (Alam et al. 2020; Park et al. 2011).

The present study was conducted to compare the e�ciency of various organic fertilizers for the recovery of mines degraded soils and the uptake, availability,and translocation of PTEs in pea plant.

Materials And MethodsSoil samples collection

Soil samples were  collected near mining sites including soap stone mines (SSM), manganese mines (MM), quartz mines (QM) and chromite mines (CM) from0-25 cm depth at 0-20 m interval. Six sub samples were collected from each mining site and thoroughly mixed to make a compsite sample. Further, thehomogenized samples were air dried and passes through 2-mm sieve. Physiochemical characteristics comprising pH, electric conductivity (EC) and organicmatter contents (OM) were determined for each sample separately. The soil was then analyzed for total metal concentrations using standard method(Nezhad et al. 2014). For PTEs analysis, 0.5 gm of soil samples were digested with aqua regia, after digestion the soil samples were cooled to roomtemperature, �ltered and diluted with distilled water and concentration of metals were determine by using, Atomic Absorption Spectroscopy (AAS-Perkin-Elmermodel 2380).

Growing media preparation for pea plants 

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Mine soils from CM, SSM, QM, MM were mixed separately with garden soil. These mixtures were then amended separately with three different compostsincluding vermicompost (VC), leaf compost (LC), and spent mushroom compost (SMC) at 1:1:1 ratio. 5 kg of each separate growing media were then �lled inplastic pots. A composite sample from each mining soil and composts were sampled for analyzing its various characterisitics (Table 1).

Pea (Pisum sativum cv. Peshawar local) was sown in pots containing growing media inside the green house. Two seeds were sown in each pot. After sowing,appropriate agronomic practices were performed throughout the experiment. All pots were regularly irrigated with distilled water to maintain the minimumrequired water level. Some plant growth and yield attributes including, days to seed emergence, plant height, stem diameter, chlorophyll content, fresh weight,dry weight, pod length, no of pods plant-1, no of seeds pod-1 and 100 seeds weight were acquired during the course of study. 

Preparation of pea seeds for PTEs analysis

Once the pea pods were ready for harvesting, pods were randomly selected and collected separately from each treatment in replicates in sterile bags andbrought to the laboratory. Seeds from pods were carefully removed and kept in sterile bags. They were then washed with distilled water and then dried in ovenat 70 oC. The dried seeds were grounded to powder. For further analysis of PTEs in the samples, 0.5 g of powdered sample was taken in digestion tubes, with10 ml of concentrated Nitric Acid (HNO3) and kept overnight at 24±2 oC. Then, 5ml Perchloric acid (HClO4) was added and kept in digestion chamber, untilcomplete digestion happened with the appearance of white fumes. The digested samples were cooled down and �ltered. Then, the volume was raised to 50 mlby adding distilled water (Alam et al. 2020; Khan et al. 2010). Finally, PTEs analysis was performed with the help of Atomic absorption spectroscopy (AAS-Perkin-Elmer model 2380).

Plant transfer factor

The soil to plant transfer of PTEs was calculated using following formula

Average daily metals intake

To know the average daily intake (ADI) of toxic metals through the consumption of peas that were cultivated on mixed soil, the following formula was used(Alam et al. 2018; Khan et al. 2016)

In the above formula, ADI is the average daily metals intake, Cmetal indicatess the amount of metals in peas (mg kg-1), Cfactor is conversion factor (fresh plant

into dry weight) which is 0.085,  Dfood intake  is intake of peas on daily basis when it is available (0.345 kg person-1 day-1) and BWaverage weight is the consumersaverage body weight 75 kg (Khan et al. 2010).

Health risk Assessment

Health risk index (HRI) is normally computed to determine the risk of toxic metals associated with the consumption of contaminated vegetables in daily diet.Actually, these are not accurate values but rather an estimation of risk associated with consumption of contaminated vegetables. HRI was calculated by usingthe following formula.

Where, ADI is average daily dietary intake of metal through contaminated vegetables and RfDo is oral reference dose value (mg kg-1 d-1), which is a safe levelof human exposure for life time. RfDo values were taken from USEPA (2006).

The Cancer risk assessment (TCR) and non cancer risk (target hazard quotient (THQ) was assessed for the potential consumers of the vegetable grown incontaminated soil amended with different organic material using the following formula.

In the equations, MC is metal concentration, I is ingestion rate (255 g person-1 day-1), EFr represents exposure frequency (350 days year-1), ED is the totalexposure duration (70 years), BW represent average body weight, CPSo is carcinogenic potency slope (μg g-1 day-1)  and AT is average time (ED × 365 daysyear-1)

Quality control

The plant (GBW07603-GSV-2) and soil (GBW07406-GSS-6) certi�ed reference materials were used to determine the accuracy of the extraction and subsequentmeasurements. The PTEs recovery was good for Cd (91.2±3.4%), Cr (90.7±3.1%), Mn (94.6±2.6%), Pb (92.4±2.9%) for plants and Cd (89.4±1.6%), Cr

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(90.1±2.2%), Mn (92.5±1.8%), Pb (90.9±2.5%) for soil. 

Statistical Analysis

The experiment was carried out in Completely Randomized Design with two factors replicated three times. All the data were analyzed using Statisticalpackage, Statistix version 8.1. When data were found signi�cantly different then least signi�cant difference at 1 % level of signi�cance was performed byusing LSD test. Graphs were prepared using sigma plot 10.0.

Results And DiscussionSoil and organic amendment physiochemical characteristics

The soil collected for pot experiment was neutral to slightly alkaline in nature and pH was different for different mine soils. The pH of CM, SSM, QM and MMwas 8.09, 8.13, 7.76, and 8.11, respectively while having EC of 0.15, 0.14, 0.18, and 0.17, for CM, SSM, QM and MM, respectively with organic matter content of2.1-2.23%. For organic fertilizer pH of VC, LC and SMC was 8.17, 8.11, and 7.85 with EC 0.12, 0.13, and0.19, respectively. High Cd, Cr, Mn, and Pb concentrationwas presented in soil (Table 1 and Fig. 1). The additions of organic fertilizers had variable effect on soil pH, EC, and PTE concentrations. After harvesting anincrease in soil pH was observed for VC (8.23), LC (8.18) and SMC (8.12). Organic amendments increased soil pH because of their alkaline nature, dissolutionof their carbonates and oxidesin amended soil. Increase in pH reduces bioavailability and mobility of PTEs in soil (Hargreaves et al. 2008). Khan et al.(2013a,b) reported that with the addition of compost to contaminated soil an increase in the pH (4.0 to 5.4) was observed and signi�cantly increase in EC(38.7 to 992 µS/cm) was reported. The soil pH play an important role in the bioavailability   and plant bioaccumulation of PTEs. In another study it wasreported that biochar application increased the soil pH, which in turn immobilized PTEs (Beesley et al. 2010; Khan et al. 2020). Similarly the addition oforganic amendments can increase the content of essential nutrients such as phosporous (P), potacium (K), Boron (B), Magnisium (Mg), Calcium (Ca) andsodium (Na), as well as reduce the solubility, bioavailability and accumulation of metals in plants (Walker and Schüßler 2004). The higher post harvest PTEsconcentration in amended soil compared to contaminated soil indicated that compost application have signi�cant effect on PTEs mobility and bioavaility(Fig. 1). The compost resulted in immobilization of PTEs may be attributed to increase in pH and formation of metals complexes. Previous studies revealedthat application of compost to contaminated soil signi�cantly increased soil pH and resulted in metal immobilization (Soares et al. 2015), attributd to thepresence of higher concentration of organic corbon in the compost (Beesley et al. 2014). The application of organic amendments is an important approach forthe immobilization and remediation of toxic metals in contaminated soil (Angelova et al. 2013).

Effect of organic amendments on plant physiological parameters

In current study the organic fertilizers has shown good results when mixed with mine soils on plant physiological parameters i.e. days to seeds emergence,plant height, stem diameter, chlorophyll content, fresh weight, dry weight, pod length plant-1, number of pod plant-1, number of seeds pod-1 and 100 seedweight (Table 2). Results indicated that amendment of organic fertilizers has both synergistic and antagonistic effect on plant physiological propertiesdepending upon the type of soil and amendment used. Decreases of days to seed emergence were observed with all the amendments in all contaminatedsoils. The highest decrease of 27.8 % with the application of VC in MM was observed. The results were similar to Wang et al. (2003), who also reported adecrease in days to seed emergence. The maximum increase in plant height  was observed in VC amended GS, while the maximum decrease, compared tocontrol, in plant height  was observed in QM with no amendement. The decrease in plant height   might be due to the effect of PTEs present in the soil that itcan limit the growth of plants and �nally effect its productivity (Sha�q and Iqbal 2005; Shanker et al. 2005). PTEs present in soil severaly affect theavailability and accumulation of essential nutrients by plants, thus affecting their growth (Khan et al. 2016; 2019). The highest increase of stem diameter wasobserved in GS amended with VC. These results were similar to the �ndings of Arancon et al. (2005) and Atiyeh et al. (2000), while the decrease in stemdiameter was observed in soil contaminated with QM. Similarly, signi�cant increase was observed in chlorophyll content of pea plant cultivated in VCamended GS.. our �nding was in agreement with that of Arancon et al. (2005), who reported that vermicompost not only increases the plant growth, but canalso enhance the chlorophyll contents in most of the vegetables. Like other plant growth attributes plant grown in QM contaminated soil resulted in decreaseof chlorophyll content compared to control.  Fresh weight and dry biomass showed similar effecst to mine impacted and compost amended soils. Themaximum weight was observed for plant grown in VC amended GS, while, unexpectedly, maximum decrease was oobserved in SMC amended QM soil. Theseresults are in agreement with the �ndings of Edwards et al. (2007). The proportion of grain to straw in the yield improves with the addition of compost andalso increased the total dry biomass of the crops. A decrease in biomass after compost amendement was reported by Manivasagaperumal et al. (2011). 

The effects on pea pod is an important factor for agronomic purposes, because changes in pods parameters have a direct impact on productivity andeconomic of the formers. In this study, the impact of compost amendment was observed on pod length, numbers of pods, number of seed per pod ans seedweight was observed and the results revealed that pod length showed maximum increase under VC amendments, while pod length was decreased in mineimpacte3d soil, with maximum decrease in CM, similarly number of pods plant-1 also showed maximum variation with the application of VC. Maximumincrease in number of seeds pod-1  and 100 seeds weight was observed in plants grown in VC amended GS. The results revealed that VC was the mosteffective treatment to improve plant growth, survival and biomass production. The results were more satisfactory when the VC was applied to soil with no orlow contamination. This is because in contaminated free soil compost improve the fertility thus enhancing plant growth, while in contaminated soil most ofthe compost served to immobilized PTEs by forming metal complexes, along with improving soil basic physiochemical parameters (Table 2). Previously it wasreported  that amendment of PTEs contaminated soil with compost reduced PTEs uptake and improve plant survival (Gadepalle et al. 2007). Soil organicmatter has the potential to bind toxic metals and moderate soil toxicity (Datta et al. 2001). Duong et al.  (2013) reported that application of compost canimprove the soil quality and productivity as well as sustainability of agriculture production. Organic matters play important role in improving chemicals,physical and biological properties of the soil. Soil organic matter and clay particles can bind each other to improve soil structure. Compost amendmentimproves soil structure by reducing bulk density and increases the soil porosity and water holding capacity of the soil (Ngo et al. 2011; Song et al. 2015). 

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PTEs in Pea seeds and compost effects

PTEs concentration in pea seeds cultivated in contaminated and compost amended soil showed signi�cant variations (p<0.01). The highest concentration ofCd, Cr, and Pb were reported in CM contaminated soil, while Mn was reported in MM contaminated soil (Fig 2). The application of VC, LC, and SMC showedsigni�cance (p<0.01) reduction in the bioaccumulation of PTEs in pea seeds. The organic fertilizers amendments had varying effects on PTEs uptake by peaplant. Toxic metals bioaccumulation was e�ciently reduced in all the treatments as compared to contaminated soil. The result indicated that the amendmenthad good effects on restricting PTEs uptake by pea plant depending upon amendment used. The results showed that a higher reductions were observed in theaccumulation of selected PTEs in VC amended soil Among the various composts CM amended with VC was the most e�cient in decreasing PTEsconcentration in pea seeds. Cd concentration was reduced from 0.98 mg kg-1 in CM contaminated soil to 0.13 in VC amended soil (87% reduction), while Crconcentration was reduced from 2.98 mg kg-1 in CM contaminated soil to 1.94 mg kg-1 in VC amended soil (35% reduction). Similarly, in Mn uptake wasreduced with the application of VC from 19.67 in MM contaminated soil to 8 mg kg-1 in VC amended soil (59% reduction) and Pb concentration was reducedfrom 0.33 in CM contaminated soil to 0.18 mg kg-1 with VC application (45% reduction). The average highest reduction was shown by VC with the applicationof CM (Fig. 2). Among the selected PTEs the maximum reduction for Cd and Pb was observed in VC amended GS, for Cr in VC amended SSM contaminatedsoil and for Mn in VC amended CM contaminated soil. The maximum reduction in Cd concentration by VC, LC and SMC was observed in MM contaminatedsoil, Pb concentration was signi�cantly reduced by VC in MM contaminated soil and LC and SMC in QM contaminated soil. Almost, similar reduction in Cr andMn bioaccumulation was observed in compost amended soil compared to mine impacted soil.

Overall, our experiment showed that the accumulations of Cd, Cr, Mn, and Pb were reduced e�ciently in pea seeds following VC, LC, and SMC amendment.Among these three amendments, VC application showed the best results in decreasing the accumulation of PTEs in pea seeds, as compared with othercomposts (LC and SMC). Our results are supported by the �ndings of Walker & Schüßler(2004) who reported that organic applications reduced the solubilityand bioavailability of PTEs in contaminated soil, by forming metals complexes (Barancikova and Makovnikova 2003). It might be due to the increase in thesoil pH with different amendments which ultimately reduces its concentration. Same observations were recorded by Bian et al. (2013), who reported asigni�cant decrease (20-90%) of Cd in rice grains with the application of VC. Soil health and fertility are closely associated with vermicompost as it containshigh nutrients (Suthar 2005). At higher pH (>6), sulphur oxide charge increases with the chelation of organic matter and the precipitation of metal hydroxidesthat reduces the concentration of metal ions (Mouta et al. 2008). The addition of organic fertilizers maintains a positive nutritive balance and enhances soilquality (Medina et al. 2006). Due to compost the free ions chelate make strong bonds with the PTEs, increase the soil pH and EC thus reduced metalbioavailability and uptake by plants. The application of compost has the ability to bind metals and the plants do not accumulate them and thus plants havebetter growth and yield. The application of organic compost led to the effective binding of phyto accessible form of different PTEs in soil and makes themunavailable to plants (Angelova et al. 2010). Organic matter decomposition results in a reduction in the mobility of metals in the soil and release salts ofphosphates, and carbonate minerals, which help in the formation of insoluble metal complexes (Walker & Schüßler 2004). Roberts et al. (2007) and Singh andSharma (2003), reported that the application of vermicompost increased the crop yield, soil nutritional status and nutrients uptake, and reduced the effect oftoxicity. Through adsorption reaction PTEs immobilize in soil with the addition of organic fertilizers. This may be due to the bindings of metal compounds(Khan et al. 2017). 

Plant transfer factor

The soil to plant transfer (PTF) of PTEs in contaminated and amended soil are given in Fig. 3. The PTF values showed great variation among different PTEsand amendements used. The soil to plant transfer of PTEs depends on soil physiochemical parameters including pH, EC, soil organic matter, soil structure andtexture, geology, climatic factors and types and concentration of amendments used (Khan et al. 2017). In the present study the PTF values were less than 1 formost of the treatments , few exception. The PTF values for Cd and Pb was less than 1 for all treatments and showed great variation for different minecontaminated and compost amended soils. In case of Cr the GS has PTF greater than 1 (1.02, while for Mn the PTF values of MM and SMC amended GS wasgreater than one (1.12 and 1.03, respectively). Among the selected PTEs the maximum PTF values for Cd, Cr, Mn and Pb were 0.79, 1.02, 1.12 and 0.082,respectively, while the minimum values were 0.08, 0.20, 0.29 and 0.016, respectively. Results revealed that among different amendements VC amended soilshowed lowest PTF values indicated the maximum metal retention capability of VC. Similarly, when compared with GS and mine impacted soil the PTF valuesof compost amended soil was signi�cantly (p<0.01) lower. The PTF values of Cd in GS was 0.30 while the GS amended with VC, LC and SMC has 0.08, 0.13and 0.12, respectively, similarly, the CM (0.73) has much greater PTF values compared to CM amended with VC (0.17), LC (0.63) and SMC (0.58). othertreatments and PTEs also showed similar variation in contaminated compared amended soil PTF values (Fig. 3). In order to assess the exposure and healthrisk of contaminated vegetables PTF is an important components to be considered.   

Health risk reduction 

Human beings are exposed to PTEs contamination through various exposure pathways, including ingestion of contaminated food and water. Plant grown inmetals contaminated soil are consumed by the local residents will, certainly,  ingest these PTEs resulting in various health disorders. The average dietaryintakes (ADI) values (mg kg-1 d-1) for individuals by consumption of pea plants grown in soils with different organic amendment are given in Table 3. The ADIvalues of different metals in contaminated and amended soils showed substantial variation, for both children and adults, depending upon amendments used(Table 3). although substantial variation was observed in ADI values for different contaminated and amended soil cultivated pea plants, all the values werebelow the critical limit (ADI<1). The highest ADI values for all the studied PTEs both children and adults were reported pea plant grown in CM contaminatedsoil except for Mn, while the lowest ADI values of PTEs through the consumption of pea seeds was observed in soil amended with VC. For instance, areduction of  3-59%, 18-25%, 27-36%, and >100%, for Cd, Cr, Pb, and Mn respectively, was observed in plants grown in compasted amended CM soil comparedto contaminated soil, while in compost (VC, LC, SMC) amended SSM soil  the Cd, Cr, Pb and Mn dietary intake was reduced by 7-58%, 18-32%, 12-32%, and 3.8-

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7.3 folds,in respectively. Consumption of pea plants grown in QM soil amended with compost (VC, LC, SMC) showed a reduction of 3-42%, 13-21%, 21-49%,and 6-33% for Cd, Cr, Mn and Pb respectively. Similalry, the ADI was reduced by 1.65-56%, 16-23%, 4.74-8 folds and 25-40% for Cd, Cr, Mn, and Pb respectivelyfor pea plants cultivated in compast amended MM soil.

HRI values of different PTEs amended with different composts are given in Table 4. HRI values less than 1 showed that the material is assumed to haveminimal acceptable risk. HRI were found less than 1 for for both children and adults in all contaminated and amended soils including control. Among the mineimpacted soil, the highest HRI was observed for CM contaminated soil followed by MM. Similarly in different amendments VC was the most effective inreducing the potential health risk through consumption of contaminated vegetables in all contaminated vegetables.  among different age groups children weremore at risk compared to adults. The THQ is often used as a tool for assessment of potential health risks resulting from consumption of metal contaminatedfood. The THQ values calculated for pea seeds are presented in Table 5. Both increasing and decreasing paterns were observed in THQ values of differentamendments as compared to contaminated and control soil. The THQ for Cr and Mn was >1 for all treatments, while for Cd in all treatments except for VCamended GS. Similarly for Pb all the treatments have THQ<1.  Comparatively, the VC amendments have signi�cant effects on PTEs bioaccumulation by peaplants and their subsequent dietary intake and human health effects. Although, higher THQs (>1) was reported for all the treatments and PTEs, except for Pb,asigni�cant reduction was observed in pea plants cultivated in compost amended soil particularly VC. TCR values for Cr and Pb is presented in Table 5. TheTCR value was not calculated for Cd and Mn because we could not found any CPSo values for these two elements. The TCR vales for both children and adultswere below the critical limit of 1 indicated minimal exposure and risk. The highest TCR values for Cr were 1.01E-02 and 6.75E-03 in children and adults,respectively, while for Pb were 1.91E-05 and 1.27E-05, respectively. Like other risk indices the maximum reduction was observed with application of VC. 

Food chain is one of the most important pathways to PTEs exposure through the consumption of contaminated vegetables (Khan et al. 2008, 2016). Theconsumption of toxic metals in vegetables grown on contaminated soil can be managed by the application of organic fertilizers and thus ADI, HRI and THQand TCR can be reduced. In the present study, among different amendments, VC was the most effective treatment to reduce the plant metal uptake and theirsubsequent health risks. 

ConclusionsOrganic fertilizers, such as VC, LC, and SMC have substantial impact on contaminated soils and can play important role in sustainable farming system byimproving the yield and biomass of food crops, the soil structure, nutrient availability, metal retention and minimizing the human health risk. It is observed thatthe application of VC showed maximum decrease in Cd, Cr, Mn, and Pb availability in pea seeds among the three amendments, followed by LC and SMC. Theresults of the present study show that the use of all the tested organic composts decreased the bioavailability of PTEs concentration in soil and theirsubsequent bioaccumulation in pea seeds. As a consequence, vegetable growth, chlorophyll content and biomass production was enhanced. The ADI, HRI,THQ and TCR (Cr and Pb only) of selected PTEs  for different age groups were also signi�cantly reduced by the application of organic fertilizers. The result ofthis study indicate that the use of organic amendments such as VC could be an effective management stratigy for reducing PTEs uptake in food plants andtheir dietary exposure.

DeclarationsCon�icts of interest

The authors has no con�ict of interest

Funding statement

This research was �nancially supported by the institutional Funding Committee at Najran University, Kingdom of Saudi Arabia under grant numberNU/IFC/ENT/01/011.

Acknowledgement

Authors would like to acknowledge the support of the Deputy for Research and Innovation- Ministry of Education, Kingdom of Saudi Arabia for this research.

 

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TablesTable 1 Characteristics of organic fertilizers and mining soil used in the study (Alam et al., 2020)

Parameters pH EC (mscm-1) OM (%) Cd(mg kg-1) Cr (mg kg-1) Mn (mg kg-1) Pb (mg kg-1)

GS 7.65 0.17 68 1.26 4.03 18.4 7.20

CM 8.10 0.19 2.10 2.62 13.60 34.7 18.0

SSM 8.00 0.18 2.15 2.46 9.81 40.9 23.3

QM 7.99 0.20 2.23 2. 59 11.2 36.5 16.4

MM 8.15 0.21 2.19 2.35 10.5 59.2 17.8

VC 8.28 0.18   0.12 0.13 1.20 0.16

SMC 7.99 0.17   0.17 0.19 1.30 0.20

LC 8.09 0.19   0.15 0.11 1.00 0.19

Table 2: Different growth parameters of pea plant as affected by organic amendments and mine soil.

Treatments Days toseedsemergence

Germinationpercentage

Plantheight(cm) 

Stemdiameter(cm) 

Chlorophyllcontent(SPAD)

Freshweight(g)

Drybiomass(g) 

Podlength(cm)

Numberof podsplant-1

Numberofseedspod-1

100Seedweight(g)

Survivalpercentage

GS 7.00 77.00 36.40 0.47 50.67 9.83 2.70 6.03 4.30 7.00 18.47 65.50

CM 10.30 60.00 30.07 0.27 40.23 7.60 2.27 4.77 3.30 3.00 9.64 52.30

SSM 10.70 65.00 32.37 0.37 40.47 7.93 2.37 5.57 3.30 4.70 17.83 51.50

QM 11.00 56.70 26.00 0.23 38.40 7.53 2.40 5.13 2.70 4.00 9.98 50.80

MM 9.70 55.00 35.67 0.27 45.93 8.53 2.43 5.53 3.00 4.30 17.83 49.30

GS+VC 5.70 88.30 38.03 0.73 53.60 10.83 2.93 6.53 5.30 8.00 21.70 85.10

GS+LC 6.30 80.00 36.70 0.50 53.37 10.70 2.87 6.30 4.70 7.70 19.17 71.70

GS+SMC 7.00 80.00 36.50 0.50 53.33 10.10 2.80 6.03 4.70 7.00 18.53 67.70

CM+VC 8.30 66.70 34.80 0.47 40.87 9.77 2.63 5.57 3.70 7.30 13.67 62.20

CM+LC 8.00 66.70 33.23 0.40 42.03 7.70 2.30 5.40 3.30 4.70 17.33 60.60

CM+SMC 8.00 66.70 32.57 0.30 42.30 8.40 2.53 5.43 3.30 5.00 16.67 56.10

SSM+VC 7.70 76.70 32.67 0.40 42.77 9.47 2.53 5.33 3.70 7.00 15.33 66.40

SSM+LC 7.30 70.00 34.23 0.40 43.57 8.20 2.47 5.43 3.70 5.00 16.67 65.00

SSM+SMC 7.70 65.00 34.87 0.37 41.77 9.13 2.47 5.23 3.30 5.00 13.30 56.90

QM+VC 9.00 73.30 33.80 0.47 41.73 9.60 2.63 5.53 3.30 6.00 18.10 65.00

QM+LC 9.00 63.30 34.40 0.33 40.00 9.23 2.50 5.13 3.70 4.70 14.12 61.20

QM+SMC 8.70 61.70 31.87 0.33 41.30 7.20 2.03 5.30 3.30 5.00 11.67 48.20

MM+VC 7.00 76.70 36.30 0.43 47.57 9.70 2.57 5.63 4.30 6.00 18.17 67.00

MM+LC 7.70 76.70 35.30 0.47 46.47 7.97 2.63 5.63 4.00 7.00 16.02 62.90

MM+SMC 8.70 71.70 30.63 0.47 44.13 8.63 2.50 5.53 3.30 6.00 17.90 58.60

Table 3: The average daily intake of metals through consumption of pea grown in mine impacted and compost amended soil

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Cd Cr Mn Pb

Child Adult Child Adult Child Adult Child Adult

GS  2.05E-04 1.53E-04 1.25E-03 9.34E-04 6.05E-03 4.53E-03 1.69E-04 1.26E-04

CM 5.91E-04 4.42E-04 1.80E-03 1.34E-03 1.14E-02 8.51E-03 1.99E-04 1.49E-04

SSM 5.79E-04 4.33E-04 1.73E-03 1.29E-03 1.15E-02 8.57E-03 1.93E-04 1.44E-04

QM 5.31E-04 3.97E-04 1.62E-03 1.21E-03 1.06E-02 7.94E-03 1.81E-04 1.35E-04

MM 3.44E-04 2.57E-04 1.73E-03 1.29E-03 1.19E-02 8.87E-03 1.93E-04 1.44E-04

GS +VC 7.84E-05 5.87E-05 1.20E-03 8.98E-04 5.77E-03 4.32E-03 1.09E-04 8.12E-05

CM+VC 2.41E-04 1.80E-04 1.35E-03 1.01E-03 4.82E-03 3.61E-03 1.27E-04 9.47E-05

SSM+VC 2.41E-04 1.80E-04 1.17E-03 8.75E-04 5.57E-03 4.16E-03 1.33E-04 9.93E-05

QM+VC 3.08E-04 2.30E-04 1.28E-03 9.56E-04 5.43E-03 4.06E-03 1.21E-04 9.02E-05

MM+VC 1.51E-04 1.13E-04 1.33E-03 9.97E-04 1.08E-02 8.04E-03 1.15E-04 8.57E-05

GS+LC 1.15E-04 8.57E-05 1.23E-03 9.20E-04 6.51E-03 4.87E-03 1.27E-04 9.47E-05

CM+LC 5.73E-04 4.29E-04 1.41E-03 1.05E-03 6.31E-03 4.72E-03 1.39E-04 1.04E-04

SSM+LC 5.07E-04 3.79E-04 1.36E-03 1.02E-03 9.49E-03 7.10E-03 1.63E-04 1.22E-04

QM+LC 5.13E-04 3.83E-04 1.34E-03 1.00E-03 6.92E-03 5.17E-03 1.33E-04 9.93E-05

MM+LC 3.38E-04 2.53E-04 1.40E-03 1.05E-03 1.14E-02 8.50E-03 1.39E-04 1.04E-04

GS+SMC 9.05E-05 6.77E-05 1.24E-03 9.25E-04 7.42E-03 5.55E-03 1.39E-04 1.04E-04

CM+SMC 5.01E-04 3.74E-04 1.47E-03 1.10E-03 7.70E-03 5.76E-03 1.39E-04 1.04E-04

SSM+SMC 5.37E-04 4.02E-04 1.41E-03 1.06E-03 8.88E-03 6.65E-03 1.69E-04 1.26E-04

QM+SMC 4.52E-04 3.38E-04 1.39E-03 1.04E-03 8.30E-03 6.21E-03 1.27E-04 9.47E-05

MM+SMC 3.32E-04 2.48E-04 1.45E-03 1.09E-03 8.94E-03 6.69E-03 1.39E-04 1.04E-04

Table 4: The health risk index of metals through consumption of pea grown in mine impacted and compost amended soil

Page 11/15

Cd Cr Mn Pb

Child Adult Child Adult Child Adult Child Adult

GS 2.05E-01 1.53E-01 4.16E-01 3.11E-01 4.32E-02 3.23E-02 4.82E-02 3.61E-02

CM 5.91E-01 4.42E-01 5.99E-01 4.48E-01 8.13E-02 6.08E-02 5.69E-02 4.25E-02

SSM 5.79E-01 4.33E-01 5.77E-01 4.32E-01 8.18E-02 6.12E-02 5.51E-02 4.12E-02

QM 5.31E-01 3.97E-01 5.39E-01 4.03E-01 7.58E-02 5.67E-02 5.17E-02 3.87E-02

MM 3.44E-01 2.57E-01 5.77E-01 4.32E-01 8.47E-02 6.34E-02 5.51E-02 4.12E-02

GS +VC 7.84E-02 5.87E-02 4.00E-01 2.99E-01 4.12E-02 3.08E-02 3.10E-02 2.32E-02

CM+VC 2.41E-01 1.80E-01 4.50E-01 3.37E-01 3.45E-02 2.58E-02 3.62E-02 2.71E-02

SSM+VC 2.41E-01 1.80E-01 3.90E-01 2.92E-01 3.98E-02 2.97E-02 3.79E-02 2.84E-02

QM+VC 3.08E-01 2.30E-01 4.26E-01 3.19E-01 3.88E-02 2.90E-02 3.45E-02 2.58E-02

MM+VC 1.51E-01 1.13E-01 4.44E-01 3.32E-01 7.68E-02 5.75E-02 3.27E-02 2.45E-02

GS+LC 1.15E-01 8.57E-02 4.10E-01 3.07E-01 4.65E-02 3.48E-02 3.62E-02 2.71E-02

CM+LC 5.73E-01 4.29E-01 4.68E-01 3.50E-01 4.51E-02 3.37E-02 3.96E-02 2.96E-02

SSM+LC 5.07E-01 3.79E-01 4.52E-01 3.38E-01 6.78E-02 5.07E-02 4.65E-02 3.48E-02

QM+LC 5.13E-01 3.83E-01 4.46E-01 3.34E-01 4.94E-02 3.70E-02 3.79E-02 2.84E-02

MM+LC 3.38E-01 2.53E-01 4.66E-01 3.49E-01 8.11E-02 6.07E-02 3.96E-02 2.96E-02

GS+SMC 9.05E-02 6.77E-02 4.12E-01 3.08E-01 5.30E-02 3.96E-02 3.96E-02 2.96E-02

CM+SMC 5.01E-01 3.74E-01 4.88E-01 3.65E-01 5.50E-02 4.12E-02 3.96E-02 2.96E-02

SSM+SMC 5.37E-01 4.02E-01 4.70E-01 3.52E-01 6.35E-02 4.75E-02 4.82E-02 3.61E-02

QM+SMC 4.52E-01 3.38E-01 4.64E-01 3.47E-01 5.93E-02 4.44E-02 3.62E-02 2.71E-02

MM+SMC 3.32E-01 2.48E-01 4.84E-01 3.62E-01 6.39E-02 4.78E-02 3.96E-02 2.96E-02

Table 5: The non-cancer and cancer risk assessment values of metals through consumption of pea grown in mine impacted and compost amended soil

Page 12/15

Cd Cr Mn Pb Cr Pb

  THQ TCR

Child Adult Child Adult Child Adult Child Adult Child Adult Child Adult

GS (ctrl) 2.31E+00 1.54E+00 4.69E+00 3.13E+00 6.82E+01 4.55E+01 4.76E-02

3.17E-02

7.04E-03

4.69E-03

1.62E-05

1.08E-05

CM 6.67E+00 4.44E+00 6.76E+00 4.50E+00 1.28E+02 8.55E+01 5.61E-02

3.74E-02

1.01E-02

6.75E-03

1.91E-05

1.27E-05

SSM 6.53E+00 4.35E+00 6.51E+00 4.34E+00 1.29E+02 8.61E+01 5.44E-02

3.63E-02

9.76E-03

6.50E-03

1.85E-05

1.23E-05

QM 5.99E+00 3.99E+00 6.08E+00 4.05E+00 1.20E+02 7.98E+01 5.10E-02

3.40E-02

9.12E-03

6.07E-03

1.73E-05

1.16E-05

MM 3.88E+00 2.58E+00 6.51E+00 4.34E+00 1.34E+02 8.91E+01 5.44E-02

3.63E-02

9.76E-03

6.50E-03

1.85E-05

1.23E-05

GS +VC 8.84E-01 5.89E-01 4.51E+00 3.01E+00 6.51E+01 4.34E+01 3.06E-02

2.04E-02

6.77E-03

4.51E-03

1.04E-05

6.93E-06

CM+VC 2.72E+00 1.81E+00 5.08E+00 3.38E+00 5.44E+01 3.63E+01 3.57E-02

2.38E-02

7.62E-03

5.08E-03

1.21E-05

8.09E-06

SSM+VC 2.72E+00 1.81E+00 4.40E+00 2.93E+00 6.28E+01 4.18E+01 3.74E-02

2.49E-02

6.60E-03

4.40E-03

1.27E-05

8.47E-06

QM+VC 3.47E+00 2.31E+00 4.81E+00 3.20E+00 6.12E+01 4.08E+01 3.40E-02

2.27E-02

7.21E-03

4.80E-03

1.16E-05

7.70E-06

MM+VC 1.70E+00 1.13E+00 5.01E+00 3.34E+00 1.21E+02 8.08E+01 3.23E-02

2.15E-02

7.52E-03

5.01E-03

1.10E-05

7.32E-06

GS+LC 1.29E+00 8.61E-01 4.63E+00 3.08E+00 7.35E+01 4.89E+01 3.57E-02

2.38E-02

6.94E-03

4.62E-03

1.21E-05

8.09E-06

CM+LC 6.46E+00 4.31E+00 5.28E+00 3.52E+00 7.12E+01 4.74E+01 3.91E-02

2.61E-02

7.93E-03

5.28E-03

1.33E-05

8.86E-06

SSM+LC 5.71E+00 3.81E+00 5.10E+00 3.40E+00 1.07E+02 7.13E+01 4.59E-02

3.06E-02

7.65E-03

5.10E-03

1.56E-05

1.04E-05

QM+LC 5.78E+00 3.85E+00 5.03E+00 3.35E+00 7.80E+01 5.20E+01 3.74E-02

2.49E-02

7.55E-03

5.03E-03

1.27E-05

8.47E-06

MM+LC 3.81E+00 2.54E+00 5.26E+00 3.50E+00 1.28E+02 8.53E+01 3.91E-02

2.61E-02

7.89E-03

5.26E-03

1.33E-05

8.86E-06

GS+SMC 1.02E+00 6.80E-01 4.65E+00 3.10E+00 8.37E+01 5.57E+01 3.91E-02

2.61E-02

6.97E-03

4.65E-03

1.33E-05

8.86E-06

CM+SMC 5.65E+00 3.76E+00 5.51E+00 3.67E+00 8.69E+01 5.79E+01 3.91E-02

2.61E-02

8.27E-03

5.51E-03

1.33E-05

8.86E-06

SSM+SMC 6.05E+00 4.03E+00 5.31E+00 3.53E+00 1.00E+02 6.68E+01 4.76E-02

3.17E-02

7.96E-03

5.30E-03

1.62E-05

1.08E-05

QM+SMC 5.10E+00 3.40E+00 5.24E+00 3.49E+00 9.37E+01 6.24E+01 3.57E-02

2.38E-02

7.86E-03

5.23E-03

1.21E-05

8.09E-06

MM+SMC 3.74E+00 2.49E+00 5.47E+00 3.64E+00 1.01E+02 6.72E+01 3.91E-02

2.61E-02

8.20E-03

5.46E-03

1.33E-05

8.86E-06

Figures

Page 13/15

Figure 1

Post-harvest heavy metals concentration in mine impacted and compost amended soils

Page 14/15

Figure 2

Heavy metals concentration in pea seeds cultivated in mine impacted and compost amended soils

Page 15/15

Figure 3

The soil to pea plant transfer factors of heavy metals