Spatial variability and temporal changes in the trace metal content of soils: implications for mine restoration plan

Assessment of environmental and carcinogenic health hazards from heavy metal contamination in sediments of wetlands

Sediment contamination jeopardizes wetlands by harming aquatic organisms, disrupting food webs, and reducing biodiversity. Carcinogenic substances like heavy metals bioaccumulate in sediments and expose consumers to a greater risk of cancer. This study reports Pb, Cr, Cu, and Zn levels in sediments from eight wetlands in India. The Pb (51.25 ± 4.46 µg/g) and Cr (266 ± 6.95 µg/g) concentrations were highest in Hirakud, Cu (34.27 ± 2.2 µg/g) in Bhadrak, and Zn (55.45 ± 2.93 µg/g) in Koraput. The mean Pb, Cr, and Cu values in sediments exceeded the toxicity reference value. The contamination factor for Cr was the highest of the four metals studied at Hirakud (CF = 7.60) and Talcher (CF = 6.97). Furthermore, high and moderate positive correlations were observed between Cu and Zn (r = 0.77) and Pb and Cr (r = 0.36), respectively, across all sites. Cancer patients were found to be more concentrated in areas with higher concentrations of Pb and Cr, which are more carcinogenic. The link between heavy metals in wetland sediments and human cancer could be used to make policies that limit people's exposure to heavy metals and protect their health.

Spatial-Heterogeneity Analysis of the Heavy Metals Cd and Pb in Road Dust in the Main Urban Area of Harbin

To provide a scientific basis for pollution prevention and control of the urban environment, the current status of heavy-metal pollution in road dust in Harbin was studied. In total, 63 road dust samples in the main urban area of Harbin were collected, and the contents of Cd and Pb, two representative heavy metals, were detected. Using the Moran Index coupled with semi-variable function and geostatistical methods, the spatial correlation, variation structure, and distribution pattern were analyzed, and the estimated probability of the heavy metals exceeding the safety standard was determined. The study showed that: The mean concentrations of Cd and Pb were higher than the background values in Heilongjiang province, and both exhibited moderate variability, while the coefficient of variation of Cd was larger than that of Pb; Cd was weakly correlated in space and randomly distributed, Pb was moderately correlated in space and exhibited good spatial structure, and both were spatially aggregated. The optimal model for fitting the variance function showed that Cd was a spherical model, and Pb was an exponential model. The variation of Cd was mainly influenced by human factors, and the variation of Pb was influenced by both structural and random factors. The optimized interpolation results of the variance function had high accuracy, and the spatial distribution of Cd was elliptical, whereas the distribution of Pb was stripe-shaped, Cd was mainly influenced by traffic factors, such as industrial enterprise distribution and road painting, while Pb was influenced by natural factors such as river sediment or the study area belonging to a geologically high background area, in addition to the above factors. The estimated probabilities indicate a higher potential risk of Cd in the northeastern part of the study area.

Short-term experiment for the in situ stabilization of a polluted soil using mining and biomass waste

Mining and biomass waste were used to remediate a brownfield affected by As, Cd, Cu, Pb and Zn pollution in a pilot scale experiment, and a plant used for phytoremediation purposes was used as an indicator of possible toxicological effects. To carry out the experiments, plots in field conditions were treated with magnesite (mining waste), magnesite-sludge compost, and magnesite-biochar respectively, while untreated soil was used as a control. The plots were then irrigated and left for one week, after which seeds of the ryegrass Lolium perenne L. were sown. Soil properties such as metal(loid) availability, pH, phosphorus availability, total nitrogen, organic carbon, and nutrients were monitored for two months. Finally, the ryegrass was harvested and pollutant concentrations were analyzed in the aerial parts. Magnesite proved to be an excellent amendment for metal(loid) immobilization, although the notable increase in soil pH and Mg content inhibited plant growth. However, the application of magnesite in combination with the sludge compost (rich in N and P) favored plant growth and also immobilized metals, although As availability increased. In contrast, the analysis of plants in this treatment revealed lower As and metal concentrations than those grown in the untreated soil. In turn, the application of magnesite and biochar was also effective in reducing metal(loid) availability; however, the plants did not grow under these conditions, probably due to the low N and P content of biochar. In this regard, the combined application of mining waste and sludge compost emerges as a useful nature-based solution for soil remediation in the context of the circular economy.

Spatiotemporal patterns and drivers of soil contamination with heavy metals during an intensive urbanization period (1989-2018) in southern China

This three-decade long study was conducted in the Pearl River Delta (PRD), a rapidly urbanizing region in southern China. Extensive soil samples for a diverse land uses were collected in 1989 (113), 2005 (1384), 2009 (521), and 2018 (421) for heavy metals of As, Cr, Cd, Cu, Hg, Ni, Pb and Zn. Multiple pollution indices and Structural Equation Models (SEMs) were used in attribution analysis and comprehensive assessments. Data showed that majority of the sampling sites was contaminated by one or more heavy metals, but pollutant concentrations had not reached levels of concerns for food security or human health. There was an increasing trend in heavy metal contamination over time and the variations of soil contamination were site-, time- and pollutant-dependent. Areas with high concentrations of heavy metals overlapped with highly industrialized and populated areas in western part of the study region. A dozen SEMs path analyses were used to compare the relative influences of key environmental factors on soil contamination across space and time. The high or elevated soil contaminations by As, Cr, Ni, Cu and Zn were primarily affected by soil properties during the study period, except 1989-2005, followed by land use patterns. Parent materials had a significant effect on elevated soil contamination of Cd, Cr, Ni, Pb and overall soil pollution during 1989-2005. We hypothesized that other factors not considered in the present study, such as atmospheric deposition, sewage irrigation, and agrochemical uses, may be also important to explain the variability of soil contamination. This study implied that strategies to improve soil physiochemical properties and optimize landscape structures are viable methods to mitigate soil contamination. Future studies should monitor pollutant sources identified by this study to fully understand the causes of heavy metal contamination in rapidly industrialized regions in southern China.

Chelate-assisted phytoaccumulation: growth of Helianthus annuus L., Vigna radiata (L.) R. Wilczek and Pennisetum glaucum (L.) R. Br. in soil spiked with varied concentrations of copper

Phytoextraction is an economic, environment-friendly and growing technology for clean-up of metal-contaminated soil. Several factors play pivotal role in making phytoextraction a successful technique. Soil fraction is an important parameter that may affect phytoextraction potential. There has been an increased realization on the role of chelates in accelerating metal uptake by plants. Thus, the present study examined the influence of different soil fractions, spiked metal concentrations and chelate dosages on Cu accumulation by Helianthus annuus L. (common sunflower), Vigna radiata (L.) R. Wilczek (mung bean) and Pennisetum glaucum (L.) R. Br. (pearl millet). To mimic the mill tailings of various mined-out sites in India, five soil fractions containing different proportions of garden soil and silica were prepared (S1: 100% soil; S2: 75% soil + 25% silica; S3: 50% soil + 50% silica; S4: 25% soil + 75% silica; and S5: 100% silica) and each fraction was spiked with known Cu (100, 250, 500 and 1000 mg kg^-1) concentration. Upon maturity of the plant, EDTA and NTA in different dosages (0.25, 0.5, 1.0 and 2.0 g kg^-1) were applied to each pot. Bioconcentration factor (BCF), bioaccumulation coefficient (BAC) and translocation factor (TF) were estimated for each set. The accumulation of Cu by H. annuus, V. radiata and P. glaucum indicated direct relation between soil fractions and harvesting periods. Better plant growth and Cu uptake were observed in pots with silica < 50% of fraction, whereas growth was arrested in pots with silica > 75%. The Cu accumulation varied significantly (p < 0.05) among the species, spiked metal concentration, chelate dosages and plant parts. Best accumulation was reported in pots with 50% soil and 50% silica either under 1.0 g kg^-1 EDTA or 2.0 g kg^-1 NTA. Irrespective of the combinations of various variables, the harvesting time affected Cu accumulation considerably. Among the species, H. annuus emerged out to be the most efficient for Cu translocation. Apparently, soil amendments facilitated enhanced uptake thereby playing an active role in improving the BAC and TF. Assisted phytoextraction is still a need until full-fledged alternatives are established in the market. The future of chelate-assisted phytoextraction seems to be limited to ex situ condition.

Meteorology drives ambient air quality in a valley: a case of Sukinda chromite mine, one among the ten most polluted areas in the world

The ambient air quality (AAQ) assessment was undertaken in Sukinda Valley, the chromite hub of India. The possible correlations of meteorological variables with different air quality parameters (PM10, PM2.5, SO2, NO2 and CO) were examined. Being the fourth most polluted area in the globe, Sukinda Valley has always been under attention of researchers, for hexavalent chromium contamination of water. The monitoring was carried out from December 2013 through May 2014 at six strategic locations in the residential and commercial areas around the mining cluster of Sukinda Valley considering the guidelines of Central Pollution Control Board (CPCB). In addition, meteorological parameters viz., temperature, relative humidity, wind speed, wind direction and rainfall, were also monitored. The air quality data were subjected to a general linear model (GLM) coupled with one-way analysis of variance (ANOVA) test for testing the significant difference in the concentration of various parameters among seasons and stations. Further, a two-tailed Pearson's correlation test helped in understanding the influence of meteorological parameters on dispersion of pollutants in the area. All the monitored air quality parameters varied significantly among the monitoring stations suggesting (i) the distance of sampling location to the mine site and other allied activities, (ii) landscape features and topography and (iii) meteorological parameters to be the forcing functions. The area was highly polluted with particulate matters, and in most of the cases, the PM level exceeded the National Ambient Air Quality Standards (NAAQS). The meteorological parameters seemed to play a major role in the dispersion of pollutants around the mine clusters. The role of wind direction, wind speed and temperature was apparent in dispersion of the particulate matters from their source of generation to the surrounding residential and commercial areas of the mine.