Study of Contaminated soil and its Treatment with Biochars of Adjacent Area of Gadoon Amazai Industrial Estate, Swabi, Khyber Pakhtunkhwa, Pakistan

Abstract

The present study was conducted to degrade accumulation of potentially toxic elements (PTEs) such as arsenic, cadmium, cobalt, chromium, cupper, manganese, nickel, lead and zinc concentration in adjacent industrial wastewater irrigated agricultural soil of Gadoon Amazai industrial estate (GAIE) with the help of remarkable type(s) and dose(s) of biochars (BCs). For this purpose, water and soil of Gadoon GAIE and adjacent area were studied. The industrial wastewater (target) and groundwater (reference) were collected for one year on monthly basis. Soil samples were collected from the agricultural fields irrigated with the industrial wastewater and groundwater. Both the water and soil samples were analysed for various physicochemical parameters and PTEs concentrations. Three type of BCs were pyrolyzed from green waste (Cynodon dactylon) at highest temperature of treatment (HTT) of 400 ºC, 600 ºC and 800 ºC and henceforth the BCs were named as 400BC, 600BC and 800BC, respective to HTT. The BCs were applied to the industrial wastewater irrigated soil at 2% and 5% rate (by weight) in a controlled condition and wheat crops were cultivated on it. After cultivation, impacts of the applied BCs on soil and wheat crops were studied. The results were evaluated through various statistical techniques like geoaccumulation index (Igeo), contamination factor (CF), pollution load index (PLI), enrichment factor (EF), ecological risk index (Er), bioaccumulation factor (BAF), translocation factor (TF) and metal pollution index (MPI). Furthermore, health risk assessment (HRA) models like average daily dose (ADD), lifetime average daily dose (LADD), noncarcinogenic health risks that as hazard risk index (HRI) and hazard index (HI) and carcinogenic health risks that is carcinogenic risk assessment (CRA) were assessed for the residents of the study area. The physicochemical results of the industrial wastewater revealed that the water has acidic pH and its total dissolved solids, total suspended solids, chemical oxygen demand, biological oxygen demand and oil and grease concentration were exceeded the maximum permissible limits(MPL) of Pakistan environmental protection agency (PakEPA, 2000). Similarly, PTEs (As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn) concentration xii were also found above the MPL of (Pak-EPA, 2000) which has made the water unfit for irrigation purpose. The industrial wastewater irrigated soil geochemical results revealed that pH of the soil is acidic due to acidic industrial wastewater discharge in to the soil. The PTEs concentrations were also above the MPL of different international standards (Bohn, 2001; Environment Protection Authority Australia, 2012; European environment agency, 2007; Ministry of ecology and environment China, 2014; Ministry of the Environment Canada, 2009; USEPA, 2002; VROM, 2000). The geostatistical results of Igeo, CF, PLI and EF revealed that accumulation intensity of PTEs were high and the Er (especially of Cd, As, Co and Pb) was at significant levels, which pose potential ecological risks to soil health. The HRI results revealed that HRIing in children is the main source of non-carcinogenic risk and can cause significant health risks. This HRIing for children contributes to 77.5% of the total HI. While CRA was found in the acceptable range. The analytical results of the wastewater cultivated wheat crops indicated that wastewater irrigation has negatively affected the germination rate, growth and yield of wheat crop. Moreover, excessive PTEs concentrations in roots, shoots, leaves and grains of wheat crop were found. Especially in grains, the Fe, Zn, Cr, Ni, Pb and Cd concentration were above their MPL of different international standards which showed free mobility of PTEs from soil to different parts of wheat grains. For human health risks, the ADDing of Cd, Pb, Cu and Mn (adults and children) and As and Ni (children) were found above the reference dose limit. Similarly, HRIing of Cd, Pb, Cu and Mn (adults and children) and As, Ni and Zn (children) were found in toxicity level, thus causing risks to human health. The physicochemical impacts of the applied BCs on the industrial wastewater irrigated soil showed that the acidic soil was changed to alkaline nature. A tremendous increase in soil physicochemical parameters was observed, such as pH (27-38%), water holding capacity with 20-45%, cation exchange capacity with 10-35%, dissolved organic carbon with 27-45%, carbon with 76-85%, nitrogen with 55-62%, phosphorus with 29- 47%, sulphur with 79-84% and potassium with 15-45%. Furthermore, PTEs concentrations has significantly (p ≤ 0.05) decreased such as, Cd (88%), Pb (87%), Cr xiii (78%), Ni (76%), Cu (69%), Mn (65%), Fe (64%), As (63%), Co (46%) and Zn (21%). The geostatistical risks of Igeo, CF, PLI, EF and Er were decreased from 12-92%, 12- 88%, 76-93%, 30-76% and 11-85% respectively for all PTEs. The health risks were decreased by 52-93% (carcinogenic) and 12-93% (non-carcinogenic) and found in the safe limit after the BCs treatments. Among the BCs and application rate, 800BC and 5% application rate have comparatively more optimum results for remediation of soil contamination than all other BCs and 2% application rate, respectively. This impacts of BCs application on wheat crops showed that bioaccumulation of all the PTEs (except Fe and Zn) were significantly (p ≤ 0.05) decreased in roots (48-95%), shoots (38-91%), leaves (30-91%) and grains (38-93%) as compared to the industrial wastewater harvested wheat crops. Conversely, growth and yield of the wheat crop was enhanced up to 6-18%, 18-38%, 17-46%, 13-45%, 15-42%, 22-55% and 34-57% for germination rate, shoot length, shoot biomass, spike length, spike biomass, grain biomass and root biomass respectively. The HRIing was significantly (p ≤ 0.05) decreased (31-93%) and was found in the safe limit (except Mn and Cu) after the BCs application. Among the BCs and application rate, 800BC and 5% application has comparatively more optimum results in control of wheat crop toxicity than all other BCs and 2% application respectively. Based on this study, the wastewater has changed the agricultural soil to toxicity level that causes significant threats to wheat crops and poses health risks in humans. So the BCs (especially 800BC with 5% application rate) should be applied for treatment of the contaminated soil, which will improve the soil quality and growth and yield of wheat crop, immobilize PTEs in soil, reduce PTEs bioaccumulation in wheat crops and will decrease human health risks caused by both the contaminated soil and wheat crop. Furthermore, wastewater irrigation should be strongly discouraged and community should be aware of the potential ecological risks associated with the wastewater irrigation.