Soil Sampling
Polluted soil from Kalakoir, Konabari, Gazipur was chosen for the experiment. The site was irrigated with the Turag river water. The river Turag is highly polluted by industrial effluents, sewage sludge, municipal waste water and urbanpollution. Five composite topsoil samples (0–20 cm depth) were randomly collected from farmer’s field (10 individual samples). The sampled soil was air- dried and passed through a 2 mm sieve to obtain homogeneous particle size.
Soil and organic amendment preparation
Two types of organic amendments were used - animal excreta category includes cow manure dust, poultry manure dust and vermicompost dust. And plant materials category includes fern dust, water hyacinth dust, mustard stover dust and barnyard grass dust. The dried organic samples were homogenized by grinding using an electric grinder. Soil samples were mixed by adding organic materials as per treatment at the rate of 5 g kg-1 soil. Samples of contaminated soil were thoroughly mixed with the organic amendments resulting in eight treatments: (i) contaminated soil + cow manure dust, (ii) contaminated soil + poultry manure dust, (iii) contaminated soil + vermicompost dust, (iv) contaminated soil + fern dust, (v) contaminated soil + water hyacinth dust, (vi) contaminated soil + mustard stover dust, (vii) contaminated soil + barnyard grass dust, and (viii) contaminated soil as control.
Experiment setup
The experiment consisted of a total of 24 plastic pots, each containing 10 kg soil. Pots were placed in a completely randomized design with three replications per treatment at a shade house of Soil Science Division, BARI, Joydebpur, Gazipur. Maize (Zea mays var. BARI hybrid Bhutta-7) seeds were sown directly in pots at a density of 6 seeds per pot on 31 December 2015. Twelve days after sowing the seedlings were thinned to 2 plants per pot. All the pots were fertilized two days before sowing with N: 90 mg kg-1 soil, P: 75 mg kg-1 soil, K: 140 mg kg-1 soil, S: 30 mg kg-1 soil, Zn: 2 mg kg-1 soil, B: 1 mg kg-1 soil. Urea, triple super phosphate, muriate of potash, gypsum, zinc sulphate monohydrate (ZnSO4. H2O) and boric acid were used as a source of N, P, K, S, Zn and B, respectively. Nitrogen was applied in two equal splits, the first split before sowing and the remaining splits at 6-8 leaf of plants after sowing. Wetting cycles (at field capacity) and air-drying every week were performed, during a period of about three months. The plant was harvested at 80 days following seeding, when it had attained reproductive maturity (before flowering). Soil was removed from the roots by careful and plants were washed with tap water followed by deionized water.
Preparation and preservation
The clean plant samples were air-dried and placed in an electric oven, dried at 85 °C for 72 h, weighed for dry biomass. The dried plant samples were homogenized by grinding using a ceramic coated grinder and used for metal analysis. Samples of contaminated soils were spread on plastic trays and allowed to dry at ambient temperature for 8 days. The dried samples of soils were ground with a ceramic coated grinder and sieved through a nylon sieve. The final samples were kept in labeled polypropylene containers at ambient temperature before analysis.
Digestion and Analytical Procedure
One gram of each sample was weighed into 50-ml beakers, followed by the addition of 10 ml mixture of analytical grade acids HNO3: HCIO4 in the ratio 5:1, and left overnight for complete contact of material. Next day, the digestion was performed at a temperature of about 190 ºC for 1.5 h. After cooling, the samples were transferred into 100 ml volumetric flask and solution was made up to a final volume raised up to the mark with distilled water. The metal concentrations were determined by atomic absorption spectrometry using a VARIAN model AA2407 Atomic Absorption Spectrophotometer (AAS). Analysis of each sample was carried out three times to obtain representative results and the data reported in µg g-1 (on a dry matter basis).
Bioconcentration factor (BCF)
To compare the accumulation and transfer of metals in the different plant parts and soils, two indices were calculated according to the procedure described by Li et al. (2009). The bioconcentration factor (BCF) was calculated according to the following equation:
BCF = [M stem or M leaves or M root]/[M soil] (1)
Statistical analysis
The experiment was designed in completely randomized (CRD) with 8 treatments and three replications. Treatment effects were determined by analysis of variance with the help of statistical package STATISTIX-10 and mean separation was tested by Tukey HSD.