Sawdust as an ameliorant to decontaminate Arsenic in potato soils

Archive of SID International Journal of Recycling of Organic Waste in Agriculture (2021)10: 77-87 Doi:10.30486/IJROWA.2021.1899077.1068 ORIGINAL RESEARCH Sawdust as an ameliorant to decontaminate Arsenic in potato soils Md. Nousad Hossain1, Tuhin Suvra Roy1, Maruf Mostofa2* Received: 06 July 2020 / Accepted: 03 February 2021 / Published online: 03 March 2021 Abstract Purpose Bangladesh is an agriculture-based country, where about 3 million ha is covered by groundwater sources for irrigation, but a significant portion of irrigation water is Arsenic contaminated. To produce Potato under Arsenic contaminated soil, an experiment was conducted to find out the effect of sawdust as an adsorbent to decontaminate Arsenic toxicity in soil. Method The research was conducted in pot experiment. It consisted of two factors. Factor A: Arsenic levels (4) viz., As0: control (0 mg/kg soil), As1: 25 mg/kg soil, As2: 50 mg/kg soil, and As3: 75 mg/kg soil. Factor B: Sawdust levels (4) viz., S0: control (0 g/kg soil), S1: 10 g/kg soil, S2: 50 g/kg soil, and S3: 100 g/kg soil. Results Arsenic content in Potato tuber peel and flesh gradually increased with the increase of Arsenic levels. As3 was found for the highest accumulation of Arsenic in tuber peel (3.867 mg/kg fresh weight) and flesh (0.6236 mg/ kg fresh weight). Arsenic content in both peel and flesh of Potato tuber decreased with increasing sawdust levels. The soil treated with S3 reduced 86.41% and 51.44% Arsenic accumulation from tuber peel and flesh, respectively, compared to control (S0). Potato produced from the treatment As1S1 accumulated a lower amount of Arsenic (0.15 mg/kg fresh weight) in Potato flesh compared to those of other treatments. Conclusion Therefore, Potato growers can produce Potato in 25 mg/kg Arsenic contaminated soil treated with 10 g sawdust/kg soil, which contains a minimum than the critical level of Arsenic for human consumption. Keywords Arsenic, Biosorbent, Sawdust, Soil, Solanum tuberosum Introduction Arsenic (As) toxicity in groundwater is a crucial issue in Bangladesh and 30 most affected districts with more than 35 million people are exposed to drinking water contaminated with Arsenic at levels above the national standard of 50 µg L-1. In Bangladesh, Arsenic concentration in groundwater ranged from <10 - >1000 µg L-1 (Hasanuzzaman et al. 2015). Arsenic contamination in groundwater was found in about 85% of the total area of Bangladesh (Haque et al. 2018). Irrigation with Arsenic contaminated groundwater is a vital source to enter Arsenic in the human food chain via the water-soil-crop-  Maruf Mostofa [email protected] 1 2 Department of Agronomy, Faculty of Agriculture, Sher-e-Bangla Agricultural University, Dhaka-1207, Bangladesh Tuber Crops Research Centre, Bangladesh Agricultural Research Institute, Gazipur-1701, Bangladesh food system (Haque et al. 2015). Recently, it has been recognized that Arsenic contaminated groundwater used for irrigation may create the same serious health hazard to people, who consume food from the irrigated crops (Geng et al. 2006), and that Arsenic accumulating in irrigated soil creates a serious threat to sustainable agriculture in affected regions (Heikens 2006). Bangladesh is predominantly an agricultural country. The people of Bangladesh not only drink the Arsenic contaminated groundwater but also irrigate their crops. The total area under irrigation is about 4 million ha, where 75% is covered by groundwater sources (Heikens 2006). About 86% of the total groundwater withdrawn is used in the agricultural sector (Huq et al. 2004). If water is contaminated, it may be threatening for plants, animals as well as for human. Irrigation is predominantly executed in the dry season for Rabi (winter) crop cultivation. Long-term irrigation with Arsenic contaminated groundwater is likely to increase its concentration in the soil as well as in crops (Ullah 1998; Huq et al. 2003). Intensive cultivation of cereal (Boro rice, Wheat, and www.SID.ir Archive of SID 78 International Journal of Recycling of Organic Waste in Agriculture (2021)10: 77-87 Maize), root crops (Potato, Sweet potato, Carrot, etc.), and vegetables require a high amount of irrigation water (Abedin et al. 2002). Total Arsenic concentration in soils is increasing day by day with an average concentration 35 to 40 mg kg-1 and a maximum of 75 mg kg-1 that can reach levels up to more than 1000 mg kg-1 (Mukhopadhyay et al. 2002). An increase of Arsenic concentrations in the cultivated medium leads to an increase in Arsenic concentration in the edible parts of vegetables (Huq et al. 2004; Shamsuddoha et al. 2005; Shaibur et al. 2009). The highest acceptable concentration of Arsenic in agricultural soil is 20 mg kg-1 (Kabata-Pendias and Pendias 1992; Hasanuzzaman et al. 2015). About 20% of crop (cereal) production was reduced due to a high concentration of Arsenic (20 mg kg-1 soil) in the plant body (Begonia et al. 1998). Arsenic accumulation in the plant parts depends on various factors, for example, plant species, soil type, soil nutrient supply, and pH (Tu and Ma 2003); among them, plant species are a significant factor. Larsen et al. (1992) observed that leafy plants accumulated Arsenic by atmospheric deposition, while tuberous plants, for example carrots and potatoes, accumulated Arsenic by both root uptake and atmospheric deposition. Potato (Solanum tuberosum L.) is one of the vital tuberous food crops in the world. In Bangladesh, it ranks 2nd after rice in production. The total area under Potato crop, per hectare yield, and total production was 0.468 million hectares, 20.61 tons per ha, and 9.6 million tons, respectively (BBS 2019). Arsenic concentration in plants varied from 0.007 mg kg-1 to 7.50 mg kg-1 (Hasanuzzaman et al. 2015). Using Arsenic contaminated irrigation water, Potato accumulated a higher concentration of Arsenic (Haque et al. 2015). People of Arsenic affected areas are consuming contaminated Potatoes, which may cause a serious health issue. Very limited researches have been done on the effects of utilizing Arsenic contaminated irrigation water or soil for Potato production and induce toxicity in Potatoes and its impact on sustainable agriculture. Arsenic cannot be destroyed easily and can only be converted into different forms or transformed into insoluble compounds in combination with other elements (Choong et al. 2007). Biosorption technology includes heavy metal removal performance for industrial wastewater, which is economical compare with others (Lee et al. 2009). It is a conventional technique for heavy metal remediation. Biosorption uses adsorbents that come from non-living biomass like sawdust, rice husk, eggshell, etc. and removes toxic metals from industri- al wastewater (Lee et al. 2009). The principal uptake mechanism generally requires unspecific ion exchange reactions. For example, positively charged groups available in the biomass structure, for instance, the amino groups, are potential reactive sites to form adsorptive complexes with negatively charged ions, for example, arsenate, arsenite, chromate, sulfate, or phosphate (Veglio and Beolchini 1997). Some works have been done to eliminate arsenate by biosorption (Hansen et al. 2006). Sawdust is a good source of biosorbent (Choong et al. 2007). It consists of carbon (60.8%), oxygen (33.8%), hydrogen (5.2%), nitrogen (0.9%), lignin, cellulose, hemicelluloses, and a minor amount of extraneous materials (5-10%) (Phonphuak and Chindaprasirt 2015). However, challenges in developing biosorbents with maximum uptake and minimum cost as well as in recognizing the biosorption mechanism remain still unexploited. The objective of the study was to determine the optimum sawdust level for reducing Arsenic accumulation in Potato in Arsenic contaminated soil. Materials and methods The study was conducted at the Agronomy Greenhouse of Sher-e-Bangla Agricultural University, Dhaka-1207, Bangladesh from November 2016 to February 2017 and November 2017 to February 2018 in Rabi season (winter season) in two consecutive years. Sufficient sunshine and comparatively low temperature prevailed throughout the experimental time (BARC 2020), which is favorable for Potato growing in Bangladesh. The research consisted of two factors viz., Factor (A): Arsenic levels (As0-4): As0 - 0 mg kg-1 soil (control), As1 - 25 mg kg-1 soil, As2 - 50 mg kg-1 soil, As3 - 75 mg kg-1 soil; Factor (B): Sawdust levels (S0-3): S0 - 0 g kg-1 soil (control), S1 - 10 g kg-1 soil, S2 - 50 g kg-1 soil, S3 - 100 g kg-1 soil. For the Arsenic treatment of soil, Sodium meta-arsenate (Na2HAsO4.7H2O) was used as the source of Arsenic. Sawdust was collected from a sawmill. The study was conducted in pot experiment (greenhouse condition) with a Randomized Complete Block Design (RCBD) with three replications, thus comprised of 48 baskets. The basket was set at 60 cm × 25 cm spacing, considering 66666 baskets were accommodated in 1 ha area. The collected soil was sandy loam. Soil pH and organic carbons were 5.6 and 0.45%, respectively. The experimental soil of basket was fertilized with a recommended dose of N, P, K, S, Zn, and B @ 57.5 µg, 34.5 µg, 75 µg, 10.8 µg, 1.8 µg, 0.875 µg, respectively, per kg soil www.SID.ir Archive of SID International Journal of Recycling of Organic Waste in Agriculture (2021)10: 77-87 79 (Mondal et al. 2011). The planting materials comprised the foundation seed tubers of Cardinal (BARI Alu-8) variety of Potato. Collected seed potato tubers were kept at room temperature to facilitate sprouting. The properly sprouted, healthy, and uniform sized (60-70 g) seed potato tubers were planted according to treatment and an entire Potato planted in a basket. Seed potatoes were planted on an average 4-5 cm depth in the basket. All the intercultural operations and plant protection standards were taken as per when required. Haulm pulling was done at 90 DAP when the majority of plants showed senescence and the tops started drying. After haulm pulling, the tubers were kept under the soil for 7 days for skin hardening. The Potatoes of each basket were separately harvested, bagged, tagged, and brought to the laboratory for further analysis. After harvesting, collected data were statistically analyzed to study the effect of sawdust and Arsenic on Potato, and evaluation of treatments for the identification of optimum sawdust level for reducing the toxicity of Arsenic from Potato tuber in Arsenic contaminated soil. The same experiment was conducted under the same treatment combination under the identical greenhouse condition in two consecutive years, and finally, the treatment means were taken from those two experiments for analysis. The tuber removed the equal volume of the water. The removed water weight was taken and the specific gravity of tuber was calculated with the following formula: Dry matter content Results and discussion The samples of tubers were collected from each treatment. After peeling off the tubers from each treatment, peel and flesh were separately dried in a drying oven at 72°C for 72 hours. Dry matter content was calculated as the ratio between dry and fresh weight and expressed as a percentage (%). The dry matter percentage was calculated with the following formula. Tuber dry matter content Total soluble solids Total soluble solids (TSS) were measured in ºbrix by refractometer. Three tuber samples were taken from each treatment to determine TSS, then calculated average value from three sample data. Specific gravity The fresh weight of the tuber was taken first. Then the samples of tuber were sunk in a full water fill beaker. Chemical analysis Potatoes were harvested and packed with labeled net bags according to treatment. After peeling the tuber, both peel and flesh samples were separated into different labeled packets. The labeled packets were immediately sent to the Analytical Laboratory of Bangladesh Council of Scientific and Industrial Research (BCSIR), Dhaka, where Arsenic was determined with an Atomic Absorption Spectrophotometer (HG-AAS) following USEPA method 1632 (USEPA 2001). Statistical analysis The mean data obtained for different characters were statistically calculated based on the method of analysis of variance (ANOVA) by using R & RStudio statistical software. The significant differences among the treatment means were compared by Fisher’s Least Significant Difference (LSD) method at a 5% level of probability. For different Arsenic levels, dry matter content of tuber peel was observed non-significant (Table 1). The dry matter content of tuber peel varied significantly with different sawdust levels. The maximum dry matter content was recorded in S3 (17.77%), which was statistically similar to S2 (17.38%) and S1 (17.12%), while the minimum was found in S0 (16.32%), which was statistically similar to S1 (17.12%) and S2 (17.38%) (Fig. 1). Dry matter content of tuber peel was significantly influenced by the combined effects of Arsenic and sawdust levels. It was observed that the highest dry matter content of tuber peel was obtained from As3S2 (19.29%), which was statistically similar to As2S2, As2S3, As1S2, As1S3, As3S1, As3S0, As0S2, As0S3, As3S3 and As1S1, whereas the lowest was recorded in As0S0 (14.47%) (Table 2). Dry matter content of tuber flesh was found non-significant for different Arsenic levels (Table 1). This research work showed distinct variations in tuber www.SID.ir Archive of SID International Journal of Recycling of Organic Waste in Agriculture (2021)10: 77-87 80 flesh dry matter content with different sawdust levels. The maximum dry matter content was recorded in S3 (16.65%), which was statistically similar to S2 (15.68%) and S1 (15.17%), while the minimum was found from S0 (13.71%) (Fig. 1). Dry matter content of tuber flesh was influenced by treatment combinations of Arsenic and sawdust levels. The maximum dry matter content (17.58%) was obtained from As2S2 which was statistically similar to As2S3, As2S1, As1S2, As3S3, As3S2, As3S1, As0S2, As0S1, As3S0 and As1S3, whereas the minimum was recorded in As1S0 (12.95%) (Table 2). Application of different levels of Arsenic had no effect on both tuber peel and flesh dry matter content but with the increasing of sawdust levels up to 100 g sawdust kg-1 soil gradually increased both tuber peel and flesh dry matter content. A higher concentration of Arsenic is toxic to plant, it influences the metabolic process, induces phytotoxicity (Haque et al. 2015) and affects different types of plant nutrients especially the phosphate through disrupting of phosphate metabolism, which ultimately reduces the uptake of P in a plant (Farnese et al. 2014). But P is essential to increase the percentage of dry matter of Potato (Fernandes et al. 2015). As a result, when sawdust levels were increased, the accumulation of Arsenic was decreased in plant and increased tuber dry matter content by uptaking more P in a plant. Specific gravity of tuber Specific gravity of tuber varied significantly with dif- Table 1 Effect of Arsenic levels on percentage of dry matter content Treatments Tuber peel dry matter content (%) Tuber flesh dry matter content (%) As0 15.02 15.94 As1 14.72 16.56 As2 16.14 17.37 As3 15.82 17.72 CV (%) 9.76 12.04 Level of significance NS NS As0: Control, As1: 25 mg As/kg soil, As2: 50 mg As/kg soil, As3: 75 mg As/kg soil. NS- Non-significance. Table 2 Combined effect of sawdust and Arsenic levels on percentage of dry matter content Treatments Tuber peel dry matter content (%) Tuber flesh dry matter content (%) As0S0 14.47 d 13.92 cd As0S1 16.22 bd 15.53 a-d As0S2 17.35 a-c 16.35 a-c As0S3 17.24 a-d 14.29 bd As1S0 16.09 bd 12.95 d As1S1 16.95 a-d 14.41 bd As1S2 17.76 a-c 16.70 a-c As1S3 17.68 a-c 14.81 a-d As2S0 15.87 cd 13.10 d As2S1 15.68 cd 16.82 a-c As2S2 19.08 a 17.58 a As2S3 18.87 ab 17.07 ab As3S0 17.35 a-c 14.88 a-d As3S1 17.37 a-c 15.9 a-d As3S2 19.29 a 15.98 a-d As3S3 17.09 a-d 16.53 a-c LSD Value 3.089 2.782 CV (%) 12.04 9.76 Level of significance * * As0: Control, As1: 25 mg As/kg soil, As2: 50 mg As/kg soil, As3: 75 mg As/kg soil, and S0: Control, S1: 10 g sawdust/kg soil, S2: 50 g sawdust/ kg soil, S3: 100 g sawdust/kg soil. * indicates 5% level of significance. www.SID.ir Archive of SID 81 International Journal of Recycling of Organic Waste in Agriculture (2021)10: 77-87 Fig. 1 Effect of sawdust levels on percentage of dry matter content S0: Control, S1: 10 g sawdust/kg soil, S2: 50 g sawdust/kg soil, S3: 100 g sawdust/kg soil. (LSD value: 1.544 and 1.391 in tuber peel and flesh dry matter content, respectively). ferent Arsenic levels. The study showed that specific gravity gradually increased with the increase of Arsenic levels. The maximum Specific gravity of tuber recorded from As2 (1.036 g cm-3), which was statistically similar to As3 (1.033 g cm-3), while the minimum was in As0 (1.014 g cm-3) (Table 3). Due to the application of different levels of sawdust, the specific gravity of the tuber varied significantly. The experiment indicated that treated with S1 (10 g sawdust kg-1 soil) produced the maximum specific gravity of tuber compared to those of other treatments and a higher dose of sawdust reduced specific gravity of tuber. The highest specific gravity (1.039 g cm-3) of tuber was recorded in S1, while the minimum (1.013 g cm-3) was found from S2 (Table 4). Specific gravity of tuber was significantly influenced by the treatment combinations of Arsenic and sawdust levels. The maximum specific gravity of the tuber was observed in As0S2 (1.063 g cm-3), while the minimum was found in As0S1 (1.005 g cm-3) (Table 5). With the increase of Arsenic levels, the specific gravity of the tuber was increased. In the case of the application of sawdust, the specific gravity of the tuber slightly increased then decreased with the increase of sawdust. A high concentration of P may decrease specific gravity (Freeman et al. 1998). So, when sawdust levels were increased, the accumulation of Arsenic was decreased and the Potato plant was able to uptake more P, which decreased specific gravity in the tuber. Total soluble solids of tuber Total soluble solids (TSS) of tuber varied significantly with different Arsenic levels. Table 3 showed that the total soluble solids of tuber decreased with increasing Arsenic levels. The maximum total soluble solid of tuber was recorded from As0 (6.375º Brix) while the minimum from As1 (5.708º Brix). Total soluble solids of tuber varied significantly with different sawdust levels. The experiment indicated that sawdust had an antagonistic relationship with the total soluble solids of the tuber. Table 4 showed that total soluble solid decreased with increasing sawdust levels. The maximum value of TSS of tuber was recorded in S0 (6.33º Brix), which was statistically similar to S1; while the minimum was found from S2 (5.5º Brix). Treatment combinations of different Arsenic and sawdust levels significantly influenced the total soluble solid of the tuber. The maximum total soluble solid of tuber was observed in As0S0 (7.0º Brix), which was statistically similar to As3S0, As1S1, and As0S3; while the minimum was found from As1S2 (5.0), which was also statistically similar to As1S0, As3S1, As3S2, and As2S3 (Table 5). Table 3 Effect of Arsenic levels on specific gravity of tuber and total soluble solids Treatments Specific gravity of tuber (g/cm3) Total soluble solid of tuber (ºBrix) As0 1.0135 c 6.375 a As1 1.0196 b 5.708 b As2 1.0359 a 5.792 b As3 1.0328 a 5.792 b LSD Value 0.0037 0.428 CV (%) 3.59 8.69 Level of significance * * As0: Control, As1: 25 mg As/kg soil, As2: 50 mg As/kg soil, As3: 75 mg As/kg soil. * Indicates 5% level of significance. www.SID.ir Archive of SID International Journal of Recycling of Organic Waste in Agriculture (2021)10: 77-87 82 Table 4 Effect of sawdust on specific gravity of tuber and total soluble solids Treatments Specific gravity of tuber (g/cm3) Total soluble solid of tuber (ºBrix) S0 1.029 b 6.333 a S1 1.039 a 5.958 ab S2 1.013 d 5.500 c S3 1.019 c 5.875 bc LSD Value 0.0037 0.428 CV (%) 3.599 8.690 Level of significance ** * S0: Control, S1: 10 g sawdust/kg soil, S2: 50 g sawdust/kg soil, S3: 100 g sawdust/kg soil. ** and * Indicate 1% and 5% level of significance, respectively. Table 5 Combined effect of sawdust and Arsenic levels on specific gravity of tuber and total soluble solids Treatments Specific gravity of tuber (g/cm3) Total soluble solid of tuber (ºBrix) As0S0 1.057 ij 7.00 a As0S1 1.005 j 6.00 bd As0S2 1.063 a 6.00 bd As0S3 1.042 cd 6.50 a-c As1S0 1.015 f-h 5.50 de As1S1 1.040 d 6.50 a-c As1S2 1.053 b 5.00 e As1S3 1.049 bc 5.83 c-e As2S0 1.013 g-i 6.00 bd As2S1 1.007 ij 6.00 bd As2S2 1.016 f-h 6.00 bd As2S3 1.018 e-g 5.16 de As3S0 1.020 e-g 6.83 ab As3S1 1.026 e 5.33 de As3S2 1.010 h-j 5.00 e As3S3 1.021 ef 6.00 bd LSD Value 0.007 0.8562 CV (%) 3.59 8.69 Level of significance * * As0: Control, As1: 25 mg As/kg soil, As2: 50 mg As/kg soil, As3: 75 mg As/kg soil, and S0: Control, S1: 10 g sawdust/kg soil, S2: 50 g sawdust/ kg soil, S3: 100 g sawdust/kg soil. * Indicates 5% level of significance. The application of Arsenic reduced the total soluble solids of tuber (Paul et al. 2014). The application of sawdust also decreased the total soluble solids of the tuber. Arsenic content of tuber peel Arsenic content of tuber peel varied significantly (P ≤ 0.01) with different Arsenic levels. Fig. 2 showed that the Arsenic content of the tuber peel gradually increased with increasing Arsenic levels. The highest arsenic content of tuber peel was recorded from As3 (3.867 mg/kg) while the minimum was in As0 (0.00 mg/kg). Fig. 2 also showed that a high positive correlation was observed between the Arsenic level in the soil and Arsenic accumulation in tuber peel (R² = 0.937**). Comparison of Arsenic accumulation of different plant parts of Potato clearly showed that the translocation of Arsenic in edible parts was relatively lower than any other plant parts. Arsenic accumulation of different plant parts was in the following sequence: root > stem > leaf > tuber, irrespective of all cultivars (Kundu et al. 2012). Arsenic concentration in Potato peel was higher than Arsenic concentration in Potato flesh (Norton et al. 2013). A higher concentration of Arsenic in soils also creates higher absorption of this element by roots, which are www.SID.ir Archive of SID International Journal of Recycling of Organic Waste in Agriculture (2021)10: 77-87 damaged and plants are restricted in growth (Onken and Hossner 1995). Arsenic content of tuber peel varied significantly (P ≤ 0.01) with different sawdust levels. Fig. 3 showed that the Arsenic content of tuber peel (mg/kg) decreased gradually with increasing sawdust levels. The highest Arsenic content of tuber peel was recorded in S0 (4.164 mg/kg), while the minimum was found from S3 (0.5658 mg/kg). The concentration of Arsenic in tuber peel drastically decreased with increasing sawdust levels (Fig. 3). Fig. 3 showed that a high negative correlation was observed between sawdust levels and Arsenic accumulation in tuber (R² = 0.902**) and there was a close negative affinity between sawdust and Arsenic accumulation in tuber peel. A plant can only uptake Arsenic as As (III) and As (V). However, it is possible when Arsenic complex hydrolysis in soil solution and make As (III) and As (V) but when sawdust or bioadsorbent was present in the soil, the As (III) and As (V) made a bond with different cellulosic organic complex with soil colloid and produced intermediate complex among Arsenic, cellulosic compound and soil colloid. In this regard, the plant could not accumulate Arsenic. Sawdust has a close affinity for heavy metal remediation from the aqueous solutions (Sud et al. 2008). The sorption of heavy metals towards biomaterials is attributed to their constituents, which are mostly carbohydrates, proteins, and phenolic compounds because they carry functional groups, for example, amines, carboxyls, and hydroxyls, which can bind to the metal ions (Choi and Yun 2006). Arsenite adsorption by the bioadsorbent (maize cob) changed with phosphoric acid/ammonia was 11 μg g−1, which corresponds to 98% removal from a 550 μg As L−1 solution for an adsorbent dose of 50 mg ml−1 ,where the maize cob changed by phosphoric acid/urea removed 0.4 μg g−1 arsenate from a 300 μg As L−1 solution (Elizalde-González et al. 2008). Arsenate and arsenite uptake by plants depends on various environmental conditions but biosorption techniques, Arsenic is removed by a biological substrate, as a sorbent, bacteria, fungi, algae, or vascular plants surfaces based on passive binding of Arsenic or other contaminants on cell wall surfaces containing special active functional groups. Hence, more works are required on addressing the molecular-level behavior of Arsenic in plants, kinetics of uptake, and transfer of Arsenic in plants with flowing waters, remobilization through decay, possible methylation, and volatilization (Vithanage et al. 2012). 83 With 5% eggshell addition, the increase in soil pH may contribute to heavy rapeseed residue, metal immobilization by altering heavy metals into more stable in soils. Concentrations of - Cd and Pb were reduced by up to 67.9 and 93.2% by the addition of 5% eggshell compared to control (Lee et al. 2013). The adsorption specificity of sawdust is Pb > Cu > Cd > Zn, where the adsorption capacity of Cu and Pb onto NaOH-treated sawdust is improved 2~3 times compare to the untreated sawdust (Lee et al. 2009). The highest biosorption capacity of the sawdust modified with ferric oxyhydroxides, evaluated by the Langmuir adsorption model, was 9.259 mg g-1 and the adsorption capacity recommending that the prepared chemically modified biosorbent has a prospect in the remediation of Arsenic from the contaminated soil water (Urik et al. 2009). The treatment combination of sawdust level and different Arsenic levels influenced the Arsenic content of tuber peel significantly (P ≤ 0.01). Arsenic content of tuber peel was observed maximum in As3S0 (6.820 mg/ kg) while no accumulation (0.000 mg/kg) was found from As0S0 (0.000 mg/kg), As0S1(0.000 mg/kg), As0S2 (0.000 mg/kg) and As0S3 (0.000 mg/kg) treatment combinations (Fig. 4). Treatment combinations of As0S0, As0S1, As0S2 and As0S3 showed that there was no Arsenic accumulation by tuber peel because Arsenic levels were controlled. Arsenic level As1 (25 mg/kg soil) was same four treatments As1S0, As1S1, As1S2 and As1S3 where As accumulation by tuber peel was (3.523, 2.1, 1.102 and 0.3967 mg/kg) where sawdust level was S0 (control), S1 (10 g sawdust/kg soil), S2 (50 g Sawdust/ kg soil) and S3 (100 g Sawdust/kg soil) (Fig. 4). Fig. 4 showed that only by increasing of sawdust level, the accumulation of Arsenic decreased in tuber peel. Sawdust acted as a bioadsorbent in soil and breakdown by microorganism with the presence of soil water and produced cellulosic waste materials viz., acetamido, amido, amino, alcoholic, carbonyl, phenolic, sulphydryl groups, etc. by microorganism with the presence of soil water adsorb Arsenic by sawdust from the Soil solution and make an intermediate complex between soil colloid and Arsenic. Sawdust has a close affinity for heavy metal remediation from the aqueous solutions (Sud et al. 2008). High bioadsorbent in soil occurred more as a bisoroption process, that’s why by increasing different sawdust levels in a particular concentration of Arsenic, Arsenic content in tuber peel decreased (Fig. 4). Result showed same trends in case of As2 and As3 Arsenic levels with S0, S1, S2 and S3 sawdust level As2S0 (6.313 mg/ www.SID.ir Archive of SID 84 International Journal of Recycling of Organic Waste in Agriculture (2021)10: 77-87 kg), As2S1 (4.43 mg/kg), As2S2 (2.277 mg/kg) and As2S3 (1.023 mg/kg), and As3S0 (6.82 mg/kg), As3S1 (4.78 mg/ kg), As3S2 (3.023 mg/kg) and As3S3 (0.843 mg/kg). Arsenic content of tuber flesh Arsenic content of tuber flesh varied significantly (P ≤ 0.01) with different Arsenic levels. Fig. 2 showed that the Arsenic content of tuber flesh increased gradually with increasing Arsenic levels. The highest arsenic content of tuber flesh was recorded from As3 (0.6236 mg/kg), while the minimum was in As0 (0.00 mg/kg). High positive correlation was observed between Arsenic level in the soil and Arsenic accumulation in tuber flesh (R² = 0.924**). Fig. 2 indicated that Arsenic accumulation in tuber flesh increased with the increasing Arsenic levels in the soil. Arsenic accumulation of different plant parts was in the following sequence: root > stem > leaf > tuber, irrespective of all cultivars (Kundu et al. 2012). A higher concentration of Arsenic in soils also creates higher absorption of this element by roots, which are damaged and plants are restricted in growth (Onken and Hossner 1995). Arsenic content of tuber flesh was strongly significant (P ≤ 0.01) with different sawdust levels. Fig. 3 showed that the Arsenic content of tuber flesh (mg/kg) decreased gradually with increasing sawdust levels. The highest Arsenic content of tuber flesh was found in S0 (0.415 mg/kg), which is while the minimum was found from S3 (0.2015mg/kg). Fig. 3 showed that a high negative correlation was observed between sawdust levels in soil and As accumulation in tuber flesh (R² = 0.902**). Arsenic Fig. 2 Linear relationship between Arsenic level in soil and Arsenic content of tuber peel and flesh As0: Control, As1: 25 mg As/kg soil, As2: 50 mg As/kg soil, As3: 75 mg As/kg soil. (LSD value: 0.1099 and 0.008426 in As content in tuber peel and flesh, respectively). accumulation in tuber flesh decreased significantly with the increase of sawdust levels as compared to control treatment (Fig. 3). Comparison of Arsenic accumulation in different levels of sawdust treatments, plant parts of Potato clearly showed that translocation of As in tuber flesh edible parts were gradually lower to S0 (0.4150 mg/ kg), S1 (0.390 mg/kg), S2 (0.2569 mg/kg) and S3 (0.2015 mg/kg) when sawdust levels were gradually higher. Treatment combination of different sawdust and Arsenic levels influenced the Arsenic content of tuber flesh significantly (P ≤ 0.01). Arsenic content of tuber flesh was observed maximum (1.083) in As3S0 while no As was found from As0S0 (0.000), As0S1 (0.000), As0S2 (0.000) and As0S3 (0.000) treatment combination (Fig. 4). The result showed similar trends in regards to As content in tuber peel. The result concluded that high bioadsorbent in soil that occurred as a more bi- soroption process, that’s why by increasing different sawdust levels in a particular concentration of Arsenic, Arsenic content in tuber flesh drastically decreased by only increasing of sawdust level. Sawdust acted as a bioadsorbent in soil and breakdown by microorganism with the presence of soil water and produced cellulosic waste materials viz. acetamido, amido, amino, alcoholic, carbonyl, phenolic, sulphydryl groups, etc., by microorganism with the presence of soil water adsorb As by sawdust from the soil solution and make an intermediate complex between soil colloid and As. Sawdust has a close affinity for heavy metal remediation from the aqueous solutions (Sud et al. 2008). As a result, when different sawdust (bioadsorbent) levels increased in soil more biosorption process occurred, then the concentration of Arsenic decreased in tuber flesh (Fig. 4). www.SID.ir Archive of SID International Journal of Recycling of Organic Waste in Agriculture (2021)10: 77-87 85 Fig. 3 Linear relationship between sawdust level in soil and Arsenic content of tuber peel and flesh S0: Control, S1: 10 g sawdust/kg soil, S2: 50 g sawdust/kg soil, S3: 100 g sawdust/kg soil. (LSD value: 0.09970 and 0.008426 in As content in tuber peel and flesh, respectively). According to the above discussion based on biosorption by bioadsorbent (sawdust), a tentative layout of minimizing the toxicity of Arsenic by biosorption technology is given below (Fig. 5). Fig. 4 Combined effect of sawdust and Arsenic levels on Arsenic content in Potato tuber peel and flesh As0: Control, As1: 25 mg As/kg soil, As2: 50mg As/kg soil, As3: 75 mg As/kg soil, and S0: Control, S1: 10 g sawdust/kg soil, S2: 50 g sawdust/ kg soil, S3: 100 g sawdust/kg soil. (LSD value: 0.1994 and 0.01685 in As content in tuber peel and flesh, respectively). Fig. 5 Tentative layout of minimizing toxicity of Arsenic by biosorption technology www.SID.ir Archive of SID 86 International Journal of Recycling of Organic Waste in Agriculture (2021)10: 77-87 Conclusion Sawdust had significant effects on quality contributing parameters of Potato. Sawdust improved the quality characters of Potato tuber, like slightly increased dry matter content, removed Arsenic content from tuber peel and flesh. The soil treated with S3 (100 g sawdust kg-1 soil) decreased 86.41% and 51.44% Arsenic accumulation through tuber peel and flesh, respectively, compared to the control (S0). Among the treatment combinations (As1S1) was suitable because, in this combination, tuber flesh accumulated 0.15 mg kg-1 Arsenic, which was lower than the critical level of Arsenic contamination, but S3 (100 gm sawdust kg-1 soil) was the best treatment for remediation of Arsenic toxicity from Potato tuber. So, Potato growers can cultivate Potato up to 25 mg kg-1 Arsenic contaminated soil using 10 g sawdust kg-1 soil. Potato production in this condition is safe for human consumption. Since Arsenic content in tuber reduced with increasing the sawdust levels, the experiment opens the door for further research to find out the exact sawdust level to minimize 100% of Arsenic from Potato tuber. Compliance with ethical standards Conflict of interest The authors declare that there are no conflicts of interest associated with this study. 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