Data for: particle size analysis and contamination indices
Description
Twenty-one soil samples taken from nine historic abandoned gold mine solid waste dump sites in the Witwatersrand Basin of South Africa were screened from a depth of 30-120 cm. On average, the particle size was 60% sand, 13% silt and 27% clay (Table S1). Metal content (mg/kg) was measured using inductively coupled plasma emission spectroscopy and reported as Pb (774.02) > As-metalloid (52.01) > U (13.89) > Ag (8.73) > Sn (2.09) > Tl (1.94) > Cd (0.20). Hg (331.61) > Au (17.84) were measured in µg/kg. The average values (mg/kg) of soluble inorganic anions were SO42- (3726.17) > NO3- (903.56) > CN- (t) (64.68) > PO43- (10.74) > NO2- (7.22). The average pH was measured at 3.89 and the EC was measured at 222.94 mS/m. Contamination factor (CF) and pollution load index (PLI) were calculated from elemental data. CF varied between various elements, from just 0.003 in one tailing to 333.500 in the next (Table S2). PLI varied from 0.289 to 2.128 between tailing dumps (Table S2). Uncontaminated sites include CF < 1 and PLI < 0. Soil screening values (SSV) (mg/kg) are Pb (2.20-7070), As (0.20-11), Hg (0.06 –2630), U (1–69), SO42- (951–8355) and CN- ( 0.51–488.25), and exceeded international soil intervention standards. NO3- (5–16,000 mg/kg) exceeded South Africa's protective water resource and informal residential area recommendations. Descriptive statistics are shown in Table S3, with the standard deviation changing significantly from 0.34 to 2149.52.
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Steps to reproduce
1. Soil sampling 1.1. Use a Global Positioning System (GPS) device to measure and record GPS coordinates for sampling points. 1.2. Take one sample upstream of each tailing dump site and another sample downstream. 1.3. Remove the top 30 cm of soil with a shovel and take 500 g of soil from a depth of 30-120 cm. 1.4. Rinse the sampling tool with distilled water between sampling stations to avoid cross-contamination. 1.5. Store the sample in a 1L amber glass container, store in a cool box and analyse the sample within 24 hours. 2. Particle size analysis Samples are dried in a 60 °C oven for 1 day and the soil is passed through a 2000 µm sieve to remove unrepresentative material, such as stones and plants, increasing homogeneity and reproducibility, and guaranteeing consistent and reliable results. 3. Emission spectroscopy using inductively coupled plasma (ICPOES) Digest a portion of the sample with diluted aqua regia, MEAN027, USEPA method 200.2 and analyse the digest. Perform the USEPA200.7 and APHA3120 methods for recoverable metals in mg/kg units in soil excluding Hg (USEPA, 2000d). Aqua regia is suitable for partially dissolving and releasing heavy metals that are potentially toxic for analysis, expressed by dry weight. To determine the HCl-soluble fraction of trace metals, accurately weigh a 2 g aliquot of a soil sample into a Teflon crucible, mix with 100 ml of 1M HCl acid, and shake at 130 rpm for 12 hours. Use Whatman filter paper to separate the soil sludge from the solution. Use filtrate for metal analysis using ICPOES: Model-GBC Quantima Sequential. 4. Calculate the contamination factor (CF), which is expressed as the ratio of the metal concentration (Cm) in the sample to the background concentration of the metal in the uncontaminated soil, obtained as the average crustal concentration (Cb). Calcualte CF according to Equation 1 as CF = (Cm) / (Cb) _______ (1). 5. Determine the geoaccumulation index (Igeo) using equation 2. Igeo = log2[Cn/(K*Bn)] _______ (2). Cn metal concentration in the investigated sample. Bn is the background concentration of the metal as determined from the global shale concentration. K = 1.5, is a constant that accounts for the lithogenic variations in the background concentration for a particular metal in the environment. 6. Calculate the Pollution Load Index (PLI) of the selected heavy metals for soil quality assessment by using the nth root of the product of the contamination factors (CF) of metals as in equation 3. PLI = (CF1 x CF2 x CF3 x · · · x CFn)^(1/n) _______ (3). 7. Calculate the potential ecological risk factor (ER) from the degree of contamination (CF) and toxic-response factor (TR) using equation 4. ER = CF x TR _______ (4). 8. Graphs and tables were created using Microsoft Office Excel, Version 16.16.27 (201012).