A new hazard assessment workflow to assess soil contamination from large and artisanal scale gold mining.

Gold mining activities are undertaken both at large and artisanal scale, often resulting in serious 'collateral' environmental issues, including environmental pollution and hazard to human and ecosystem health. Furthermore, some of these activities are poorly regulated, which can produce long-lasting damage to the environment and local livelihoods. The aim of this study was to identify a new workflow model to discriminate anthropogenic versus geogenic enrichment in soils of gold mining regions. The Kedougou region (Senegal, West Africa) was used as a case study. Ninety-four soil samples (76 topsoils and 18 bottom soils) were collected over an area of 6,742 km2 and analysed for 53 chemical elements. Robust spatial mapping, compositional and geostatistical models were employed to evaluate sources and elemental footprint associated with geology and mining activities. Multivariate approaches highlighted anomalies in arsenic (As) and mercury (Hg) distribution in several areas. However, further interpretation with enrichment factor (EFs) and index of geoaccumulation (IGeo) emphasised high contamination levels in areas approximately coinciding with the ones where artisanal and small scale mining (ASGM) activities occur, and robust compositional contamination index (RCCI) isolated potentially harmful elements (PHE) contamination levels in very specific areas of the Kedougou mining region. The study underlined the importance of complementary approaches to identify anomalies and, more significantly, contamination by hazardous material. In particular, the analyses helped to identify discrete areas that would require to be surveyed in more detail to allow a comprehensive and thorough risk assessment, to investigate potential impacts to both human and ecosystem health.

Source patterns of potentially toxic elements (PTEs) and mining activity contamination level in soils of Taltal city (northern Chile).

Mining activities are among the main sources of potentially toxic elements (PTEs) in the environment which constitute a real concern worldwide, especially in developing countries. These activities have been carried out for more than a century in Chile, South America, where, as evidence of incorrect waste disposal practices, several abandoned mining waste deposits were left behind. This study aimed to understand multi-elements geochemistry, source patterns and mobility of PTEs in soils of the Taltal urban area (northern Chile). Topsoil samples (n = 125) were collected in the urban area of Taltal city (6 km2) where physicochemical properties (redox potential, electric conductivity and pH) as well as chemical concentrations for 35 elements were determined by inductively coupled plasma optical emission spectrometer. Data were treated following a robust workflow, which included factor analysis (based on ilr-transformed data), a new robust compositional contamination index (RCCI), and fractal/multi-fractal interpolation in GIS environment. This approach allowed to generate significant elemental associations, identifying pool of elements related either to the geological background, pedogenic processes accompanying soil formation or to anthropogenic activities. In particular, the study eventually focused on a pool of 6 PTEs (As, Cd, Cr, Cu, Pb, and Zn), their spatial distribution in the Taltal city, and the potential sources and mechanisms controlling their concentrations. Results showed generally low baseline values of PTEs in most sites of the surveyed area. On a smaller number of sites, however, higher values concentrations of As, Cd, Cu, Zn and Pb were found. These corresponded to very high RCCI contamination level and were correlated to potential anthropogenic sources, such as the abandoned mining waste deposits in the north-eastern part of the Taltal city. This study highlighted new and significant insight on the contamination levels of Taltal city, and its links with anthropogenic activities. Further research is considered to be crucial to extend this assessment to the entire region. This would provide a comprehensive overview and vital information for the development of intervention limits and guide environmental legislation for these pollutants in Chilean soils.

Source patterns and contamination level of polycyclic aromatic hydrocarbons (PAHs) in urban and rural areas of Southern Italian soils.

Polycyclic aromatic hydrocarbons (PAHs) are a group of persistent organic pollutants. They have been identified as a type of carcinogenic substance and are relatively widespread in environment media such as air, water and soils, constituting a significant hazard for human health. In many parts of the world, PAHs are still found in high concentrations despite improved legislation and monitoring, and it is therefore vital defining their profiles, and assessing their potential sources. This study focused on a large region of the south of Italy, where concentration levels, profiles, possible sources and toxicity equivalent quantity (TEQ) level of sixteen PAHs were investigated. The survey included soils from five large regions of the south of Italy: 80 soil samples (0-20 cm top layer) from urban and rural locations were collected and analysed by gas chromatography-mass spectrometry. Total PAHs and individual molecular compounds from the US Environmental Protection Agency priority pollutants list were identified and measured. Results showed that 16 PAHs varied significantly in urban and rural areas, and different regions presented discordant characteristics. Urban areas presented concentrations ranging from 7.62 to 755 ng g-1 (mean = 84.85 ng g-1), whilst rural areas presented ranges from 1.87 to 11,353 ng g-1 (mean = 333 ng g-1). Large urban areas, such as Rome, Naples and Palermo, exhibited high PAHs total concentration, but high values were also found in rural areas of Campania region. Different PAHs molecular ratios were used as diagnostic fingerprinting for source identification: LWMPAHs/HWMPAHs, Fluo/(Fluo + Pyr), BaA/(BaA + Chr), Ant/(Ant + Phe) and IcdP/(IcdP + BghiP). These ratios indicated that PAHs sources in the study area were mainly of pyrogenic origin, i.e. mostly related to biomass combustion and vehicular emission. On the other hand, values in Sicilian soils seemed to indicate a petrogenic origin, possibly linked to emissions from crude oil combustion and refineries present in the region. Finally, results allowed to calculate the toxicity equivalent quantity (TEQBAP) levels for the various locations sampled, highlighting that the highest values were found in the Campania region, with 661 and 54.20 ng g-1, in rural and urban areas, respectively. These findings, which could be linked to the presence of a large solid waste incinerator plant, but also to well-documented illegal waste disposal and burning, suggest that exposure to PAH may be posing an increased risk to human health in some of the studied areas.

Decomposition of carboxymethyl cellulose based on nano-knife principle.

The traditional degradation of organic pollutants is based on the sacrifice of chemical or biological reagents. In this study, a purely physical technique was developed to break the chemical bonds and consequently decompose macromolecules in aqueous solution. Assisted with a high-speed mechanical blade, refined quartz sand grains with particularly sharp nano-scale edges can act as 'nano-knives', which are able to cut the long chain of carboxymethyl cellulose (CMC, as a model molecule). High performance size exclusion chromatography measurements evidenced that the original CMC molecules (41,000 Da) were decomposed into a series of smaller molecules (460, 1000, 2200, 21,000, 27,000 and 31,000 Da). Consequently, the initial viscosity of the CMC solution (2 g/L) rapidly decreased by approximately 50% after 3 min treatment by the nano-knife materials along with the mechanical blade. Fourier transform infrared (FTIR) spectra indicated that the original functional groups were still present and new functional groups were not produced after shearing. The intensity of the main functional group ß-1-4-glycosidic bond (wavenumber 1062 cm-1) was observed to markedly decrease after shearing. These results indicated that the long-chain CMC was cleaved into short-chain CMC. A degradation mechanism was proposed whereby the cutting force generated by the rapid motion of the nano-knives may be responsible for the breakage of ß-1-4-glycosidic bonds in the macromolecular cellulose backbone. These results provide support for a potentially more affordable and environment-friendly strategy for physical-based decomposition of recalcitrant organic pollutants from aqueous solution without the need of chemical or biological reagents.

Field method for preservation of total mercury in waters, including those associated with artisanal scale gold mining.

Analysis of mercury (Hg) in natural water samples has routinely been impractical in many environments, for example, artisanal and small-scale gold mines (ASGM), where difficult conditions make monitoring of harmful elements and chemicals used in the processes highly challenging. Current sampling methods require the use of hazardous or expensive materials, and so difficulties in sample collection and transport are elevated. To solve this problem, a solid-phase extraction-based method was developed for the sampling and preservation of dissolved Hg in natural water samples, particularly those found around ASGM sites. Recoveries of 85% ± 10% total Hg were obtained during 4 weeks of storage in refrigerated (4 °C, dark) and unrefrigerated (16 °C, dark) conditions, and from a representative river water spiked to 1 µg L-1 Hg2+, 94% ± 1% Hg recovery was obtained. Solid-phase extraction loading flow rates were tested at 2, 5, and 10 mL min-1 with no breakthrough of Hg, and sorbent stability showed no breakthrough of Hg up to 2 weeks after functionalisation. The method was deployed across five artisanal gold mines in Kakamega gold belt, Kenya, to assess Hg concentrations in mine shaft water, ore washing ponds, and river and stream water, including drinking water sources. In all waters, Hg concentrations were below the WHO guideline limit value of 6 µg L-1, but drinking water sources contained trace concentrations of up to 0.35 µg L-1 total Hg, which may result in negative health effects from long-term exposure. The SPE method developed and deployed here is a robust sampling method that can therefore be applied in future Hg monitoring, toxicology, and environmental work to provide improved data that is representative of total dissolved Hg in water samples.

The present and potential future of aqueous mercury preservation: a review.

Mercury is considered to be one of the most toxic elements to humans. Due to pollution from industry and artisanal gold mining, mercury species are present globally in waters used for agriculture, aquaculture, and drinking water. This review summarises methods reported for preserving mercury species in water samples and highlights the associated hazards and issues with each. This includes the handling of acids in an uncontrolled environment, breakage of sample containers, and the collection and transport of sample volumes in excess of 1 L, all of which pose difficulties for both in situ collection and transportation. Literature related to aqueous mercury preservation from 2000-2021 was reviewed, as well as any commonly cited and relevant references. Amongst others, solid-phase extraction techniques were explored for preservation and preconcentration of total and speciated mercury in water samples. Additionally, the potential as a safe, in situ preservation and storage method for mercury species were summarised. The review highlighted that the stability of mercury is increased when adsorbed on a solid-phase and therefore the metal and its species can be preserved without the need for hazardous reagents or materials in the field. The mercury species can then be eluted upon return to a laboratory, where sensitive analytical detection and speciation methods can be better applied. Developments in solid phase extraction as a preservation method for unstable metals such as mercury will improve the quality of representative environmental data, and further improve toxicology and environmental monitoring studies.

Investigating the potential of sunflower species, fermented palm wine and Pleurotus ostreatus for treatment of petroleum-contaminated soil.

Phyto- and myco-remediation have been identified as sustainable options for treatment of petroleum-contaminated soils. To appraise the benefits thereof, the potentials of 3 sunflower species, 2 palm wine types and P. ostreatus to treat petroleum-contaminated soils was investigated. The study involved sampling of petroleum-contaminated soils and treatment with the phyto- and myco-remediation agents for a period of 90-days. Agents used for the remediation were 3 species of sunflowers (Helianthus annus-pacino gold, Helianthus sunsation &Helianthus annus-sunny dwarf), fermented palm wine (from 2 species of palm trees -Elaeis guineensis &Raffia africana), and oyster mushroom (Pleurotus ostreatus). The study further investigated variation in remediation efficiency among the sunflower and palm wine species, as well as different substrates and conditions for optimal application of P. ostreatus. The results obtained revealed up to 340 g/kg dry weight of Total petroleum hydrocarbons (TPHs) in the soils, with remediation outcomes of up to 69% by the sunflower- Helianthus annus (Pacino gold), 70% by fermented palm wine, and 85% by P. ostreatus. While the remediation efficiency of sunflower species was proportional to biomass, there was no significant difference in remediation efficiency of the palm wines. It was also found that substrates type and method of application has a significant impact on the remediation efficiency of P. ostreatus. The study further revealed available nitrate and electrical conductivity as possible useful indicators of TPHs concentration and remediation progress in soils.

Mycoremediation of petroleum contaminated soils: progress, prospects and perspectives.

Mycoremediation, an aspect of bioremediation, has been investigated for some decades. However, there seems to be little progress on its commercial application to petroleum-contaminated soils despite some promising outcomes. In this review, mycoremediation is examined to identify development, limitations and perspectives for its optimal utilization on petroleum-contaminated soils. Mycoremediation agents and substrates that have been used for the treatment of petroleum contaminated soils have been identified, application methods discussed, recent advances highlighted and limitations for its applications accentuated. Possible solutions to the challenges in applying mycoremediation to petroleum-contaminated soils have also been discussed. From this review, we conclude that for optimal utilization of mycoremediation of petroleum-contaminated soils, ideal environmental, edaphic and climatic factors of a typical contaminated site must be incorporated into the approach from first principles. Development of application procedures that can easily translate laboratory results to field applications is also required.

Status, sources and contamination levels of organochlorine pesticide residues in urban and agricultural areas: a preliminary review in central-southern Italian soils.

Organochlorine pesticides (OCPs) are synthetic chemicals commonly used in agricultural activities to kill pests and are persistent organic pollutants (POPs). They can be detected in different environmental media, but soil is considered an important reservoir due to its retention capacity. Many different types of OCPs exist, which can have different origins and pathways in the environment. It is therefore important to study their distribution and behaviour in the environment, starting to build a picture of the potential human health risk in different contexts. This study aimed at investigating the regional distribution, possible sources and contamination levels of 24 OCP compounds in urban and rural soils from central and southern Italy. One hundred and forty-eight topsoil samples (0-20 cm top layer) from 78 urban and 70 rural areas in 11 administrative regions were collected and analysed by gas chromatography-electron capture detector (GC-ECD). Total OCP residues in soils ranged from nd (no detected) to 1043 ng/g with a mean of 29.91 ng/g and from nd to 1914 ng/g with a mean of 60.16 ng/g in urban and rural area, respectively. Endosulfan was the prevailing OCP in urban areas, followed by DDTs, Drins, Methoxychlor, HCHs, Chlordane-related compounds and HCB. In rural areas, the order of concentrations was Drins > DDTs > Methoxychlor > Endosulfans > HCHs > Chlordanes > HCB. Diagnostic ratios and robust multivariate analyses revealed that DDT in soils could be related to historical application, whilst (illegal) use of technical DDT or dicofol may still occur in some urban areas. HCH residues could be related to both historical use and recent application, whilst there was evidence that modest (yet significant) application of commercial technical HCH may still be happening in urban areas. Drins and Chlordane compounds appeared to be mostly related to historical application, whilst Endosulfan presented a complex mix of results, indicating mainly historical origin in rural areas as well as potential recent applications on urban areas. Contamination levels were quantified by Soil Quality Index (SoQI), identifying high levels in rural areas of Campania and Apulia, possibly due to the intensive nature of some agricultural practices in those regions (e.g., vineyards and olive plantations). The results from this study (which is in progress in the remaining regions of Italy) will provide an invaluable baseline for OCP distribution in Italy and a powerful argument for follow-up studies in contaminated areas. It is also hoped that similar studies will eventually constitute enough evidence to push towards an institutional response for more adequate regulation as well as a full ratification of the Stockholm Convention.

Dynamic characteristics of sulfur, iron and phosphorus in coastal polluted sediments, north China.

The cycling of sulfur (S), iron (Fe) and phosphorus (P) in sediments and pore water can impact the water quality of overlying water. In a heavily polluted river estuary (Yantai, China), vertical profiles of fluxes of dissolved sulfide, Fe2+ and dissolved reactive phosphorus (DRP) in sediment pore water were investigated by the Diffusive Gradients in Thin films technique (DGT). Vertical fluxes of S, Fe, P in intertidal sediment showed the availability of DRP increased while the sulfide decreased with depth in surface sediment, indicating that sulfide accumulation could enhance P release in anoxic sediment. In sites with contrasting salinity, the relative dominance of iron and sulfate reduction was different, with iron reduction dominant over sulfate reduction in the upper sediment at an intertidal site but the reverse true in a freshwater site, with the other process dominating at depth in each case. Phosphate release was largely controlled by iron reduction.