Shamim Al Mamun .
Department of Environmental Science and Resource Management, Mawlana Bhashani Science and Technology University, Tangail 1902, Bangladesh
Shatabdi Saha .
Department of Environmental Science and Resource Management, Mawlana Bhashani Science and Technology University, Tangail 1902, Bangladesh
Jannatara Ferdush .
Department of Environmental Science and Resource Management, Mawlana Bhashani Science and Technology University, Tangail 1902, Bangladesh
Tanmoy Roy Tusher .
Department of Environmental Science and Resource Management, Mawlana Bhashani Science and Technology University, Tangail 1902, Bangladesh
Md. Abu-Sharif .
Department of Environmental Science and Resource Management, Mawlana Bhashani Science and Technology University, Tangail 1902, Bangladesh
Md. Ferdous Alam .
Institute of Nuclear Science and Technology, Atomic Energy Research Establishment, Bangladesh Atomic Energy Commission, Dhaka 3787, Bangladesh
Megan R. Balks .
Faculty of Science, The University of Waikato, Hamilton, New Zealand
Zakia Parveen
Department of Soil, Water and Environment, Dhaka University, Dhaka 1000, Bangladesh
Cadmium, Heavy metals, Organic amendment, Biochar, Vermicompost, Health risk
Agricultural soils in Tangail district
Risk Management in Agriculture
Contamination of soil
Study area and sampling sites: The study focused on the agricultural soils in Tangail district, which is located in the central part of Bangladesh and covers an area of 3414 km2 consisting of 12 upazilas (Banglapedia 2020). Tangail district is characterized by four agro-ecological zones (AEZs), namely Active Brahmaputra-Jamuna Floodplain (AEZ-7), Young Brahmaputra and Jamuna Floodplain (AEZ-8), Old Brahmaputra Floodplain (AEZ-9) and Madhupur Tract (AEZ-28) (Kumar et al. 2018). In the first three AEZ areas, mainly rice and vegetables are grown and most of these lands remain under water during April to August, sometimes even till September and Mid October. In Madhupur Tract, mainly pineapple and vegetables are grown. The areas have a tropical monsoon climate. The average minimum temperature is 11.4 C observed in January, and the average maximum temperature is recorded as 33.8 C in April (BBS 2018), with an annual average rainfall of 1848 mm (BBS 2018) and annual average relative humidity of 80% (Akter et al. 2016). Rainfall starts mainly in April and continues until October, while about 65% of rainfall occurs during the monsoon season (June–September) (BBS 2018). According to the Department of Agricultural Extension (DAE), the district comprises 328,160 ha of agricultural land (MPSSWRD 2005) and produces about 847,309 tons of agricultural crops every year (Rahman and Mian 2016). Rice is the principal agricultural crop (65.7%), followed by oil seeds, wheat/maize, pulses, vegetables, spices, sugarcane, potato, mustard, and others (MPSSWRD 2005). Soil sample collection and analysis Although Tangail district is composed of 12 distinct upazilas, soil samples were collected from 10 upazilas for the current research which ensured that all the cropping patterns existing in Tangail district were sampled. Soil samples were collected from 60 different agricultural lands from the selected 10 upazilas of Tangail district, while the agricultural lands were selected considering various cropping patterns in the study area. Both the topsoil (0–15 cm) and subsoil (16–30 cm) were collected from each sampling site. In each sampling site, three sampling points (about 5 feet distance) were selected. From each point, one top soil and one subsoil were collected. The three subsoils from three points were mixed together to form a representative composite subsoil sample. Similarly, composite top soil samples were prepared for each sampling site. In total, 120 samples (60 topsoil and 60 subsoil) were collected from the study area. Collected samples were dried at room temperature for 2 weeks then crumbled using a porcelain mortar, sieved through a 2 mm nylon mesh, and homogenized. The samples were finally stored in clean Ziploc bags under freezing conditions until chemical analysis. The soil pH was determined using a digital pH meter (Hannah, Woonsocket, RI, USA) in a soil/water ratio of 1:2.5. Total P was determined colorimetrically using a spectrophotometer at 490 nm by developing yellow color with vanadomolybdate after collecting the extract by digestion with ternary acid mixture (conc. HNO3: conc. HSO4: HClO4 (60–62%) = 5:1:2). To get the extract, 0.5 g of dried and ground sample was taken in a 50 ml conical flask and 10 ml ternary acid mixture was added. The mixture was allowed to predigest for 24 h, heated over a low gas flame, gradually raised the heat until the mixture becomes clear. Afterward, the mixture was allowed to cool and distilled water was added to make the volume up to 50 ml (Huq and Alam 2005). For determining soil Cd concentrations, soil samples were wet-digested with aqua regia (HNO3:- HCl = 1:3) mixture under closed system (Blum et al. 1996). For analysis, 1 g of soil sample was digested with 20 ml of aqua regia and heated until the acid is dried out. Then the mixture was diluted and volumed with distilled water. The digested samples were filtered with Whatman no. 42 filter paper. Finally, the extract was measured using AAS (Shimadzu AA6800, Kyoto, Japan) at 228.8 nm (Huq and Alam 2005). Calibration curve was prepared using the certified standard solution of AAS (Wako Pure Chemical Industries, Ltd., Osaka, Japan). In Bangladesh, there is no prescribed permissible limits given by any governmental or non-governmental agencies for Cd concentrations in soils. Thus, this study used the permissible limit of Cd in soil as 1.0 and 1.4 mg kg-1 according to the Dutch soil quality standard (MVROM 2000) and Canadian environmental quality standard (CCME 2003), respectively. The level of contamination was calculated using the contamination factor (CF) by the following formula as used by several researchers (Islam et al. 2015a; Tusher et al. 2017): CF ¼ Measured Cd concentration in soil=Background concentration of Cd ð1Þ The level of contamination can be classified based on the calculated CF values as: low (CF \1), moderate (1 B CF \ 3), considerable (3 B CF \6), and high (CF C 6). The background value of Cd was considered as 0.11 mg kg-1 for Bangladesh soil (Kashem and Singh 1999).
Environ Geochem Health
Journal