Concentrations Of Potentially Toxic Metals Research Articles

Potentially toxic metals in seawater, sediment and seaweeds: bioaccumulation, ecological and human health risk assessment.

This study assesses the bioaccumulation, ecological, and health risks associated with potentially toxic metals (PTMs), including Pb, Hg, Cd, As, and Cr in Hare Island, Thoothukudi. The results revealed that the concentration of PTMs in sediment, seawater, and S. wightii ranged from 0.095 to 2.81mgkg-1, 0.017 to 1.515mgL-1, and 0.076 to 5.713mgkg-1, respectively. The highest concentrations of PTMs were found in the S. wightii compared to seawater and sediment. The high bioaccumulation of Hg and As in S. wightii suggests that it can be used as a bioindicator for these elements in this region. The ecological risk indices, which include individual, complex, biological, and ecological pollution indices, suggest that Hare Island had moderate contamination with Hg and Cd. However, there are no human health risks associated with PTMs. This study examines the current ecological and health risks associated with PTMs and emphasizes the importance of regular monitoring.

Speciation of Potentially Toxic Metals from the Mine Impacted soils: A Case Study of Riruwai Mining Area, Kano State, Northern Nigeria

Mining and smelting sectors contribute significantly to global growth on a regional and local scale. However, the operations are causing significant environmental damage, particularly pollution of the soil with potentially toxic metals (PTMs). In this study, the speciation of PTMs (arsenic, cadmium, chromium, mercury, manganese, nickel, lead and zinc) from the mine impacted soils of Riruwai mining area was investigated using a modified Tessier sequential extraction method. The findings of the study revealed that all the PTMs examined are considerably associated with non-residual fractions in all the sampling locations. This indicates that all the PTMs investigated in the study area may be highly mobile in the soils and hence potentially toxic. The concentrations of PTMs in the soil’s geochemical fractions were found to vary with the sampling locations, with active mining sites significantly (p ≤ 0.05) recording the highest value, followed by farmland, while the lowest value was reported at the control site. Therefore, to protect the environment and the health of the local populace, PTMs in the soils of the study area should be regularly monitored and a treatment program should be put in place.

Probabilistic non-carcinogenic and carcinogenic risk assessments of potential toxic metals (PTMs) and polycyclic aromatic hydrocarbons (PAHs) in canned foods in Nigeria: understanding the size of the problem

The purpose of the study was to determine the concentrations of potential toxic metals (PTMs) and polycyclic aromatic hydrocarbons (PAHs) in 20 canned food samples (fish, meat, vegetable, non-alcoholic drink and beverage) sold in markets of Port Harcourt city (Nigeria) and to assess their potential human health risks (non-carcinogenic and carcinogenic). The methodology comprised the Graphite Furnace Atomic Absorption Spectrometry (GFAAS) analysis of metals and Gas Chromatography-Mass Spectrometry (GC-MS) analysis of PAHs, and then the calculation of the estimated daily intake (EDI), target hazard quotient (THQ) and cancer risk (CR) in adults and children. Results showed that the EDI values for As, Cd, Cu, and Pb from consumption of canned foods were below the provisional tolerable daily/provisional tolerable weekly intakes (PTDI/PTWI), and for Fe and Zn below the recommended daily intake (RDI), in both adults and children. The EDI value for B[a]P from consumption of canned foods was less than the PTWI value in both adults and children. Whilst the individual THQ values of metals were less than 1, the ∑THQ values were higher than 1 thus indicating a potential health risk arising from consumption of canned foods containing a mixture of metals. Moreover, the CR values by individual carcinogenic metals indicated a priority risk in both adults and children for As (mean, 2.43E-02 and 9.73E-03) and Cd (mean, 6.03E-03 and 1.95E-03), while the risk was acceptable for PAHs exposure (2.13E-09). In addition, the total CR (TCR), which was used to assess the effects of multiple carcinogenic metals, ranged from 1.24E-02 to 6.237E-02 indicating a carcinogenic risk for adults and children. In conclusion, the consumption of canned foods by Nigerian community can bring about worst health risks due to the residual concentration of PTMs in these products and the health hazard associated with them.

Effect of multiple washing operations on the removal of potentially toxic metals from analkaline farmland soil and the strategy for agricultural reuse.

Few studies have carried out soil washing experiments using pot experiments to simulate in situ soil washing operations, particularly for alkaline soils. This study explored the effects of multiple washing operations using pot experiments on the removal efficiencies of potentially toxic metals (PTM)from alkaline farmland soil and the reuse strategy of washed soil for safe agricultural production. The results showed that the removal efficiencies of Cd, Pb, Cu, and Zn after seven washings with a mixed chelator (EDTA, GLDA, and citric acid) were 41.1%, 47.1%, 14.7%, and 26.5%, respectively, which was close to the results of the EDTA treatment. For the alkaline soil studied, the second washing with the mixed chelators most effectively removed PTM owing to the activation of them after the first washing operation. The mixed chelator more effectively increased the proportion of stable fraction of PTM and maintained soil nutrients (e.g., nitrogen content) than EDTA, indicating little disturbance of alkaline soil quality after washing with the mixed chelator. After the amendment of the washed soil, there was no visible difference in the biomass weight of crops from the soils washed with different agents, indicating that the inhibitory effect of both washing agents on plant growth was effectively alleviated. The Cd and Pb contents in Z. mays were below the threshold of Hygienical Standard for Feeds of China (GB 13078-2017) (1 and 30mg·kg-1). Moreover, after three cropping operations, the available concentrations of PTM in the soil washed with the mixed chelator were lower than those in the soil washed with EDTA, indicating the value and potential of agricultural reuse of alkaline farmland soil washed with the mixed chelator.

Human Health Risk Assessment and Histopathological Alterations in Puntius sophore of Damsal Nala, Sukinda Chromite Valley, Odisha, India

The aim of the present study was to assess the concentration of potentially toxic metals (PTMs) like As, Cd, Cr, Cu, Fe and Pb in the Damsal Nala of Sukinda Chromite Valley, Jajpur of Odisha (India) and its subsequent histopathological lesions in the fish Puntius sophore. Energy Dispersive X-Ray Fluorescence (EDXRF) and Flame Atomic Absorption Spectroscopy (FAAS) methods were used to evaluate the concentrations of PTMs in the muscles of fish, Puntius sophore collected from different zones namely upstream discharge zone (UDZ) and upstream zone (UZ) of the Damsal Nala and control water bodies (CW). In the UDZ of Nala, the concentration of metals viz., Cd, Pb and Fe were 2 to 7 times, and Cr was 77 times higher than the maximum permissible limits recommended by WHO and FAO in the fish muscles. The values of Target Hazard Quotients (THQ) of all these 6 metals were <1 in CW and UZ, but in UDZ the THQ values of Cr and Fe were >1. Hazard Index (HI) for UDZ was 3.47, indicated the alarming concentration of metal which can pose serious risk to human health. Histopathological observations in liver and kidney of Puntius sophore collected from UDZ demonstrated the serious lesions, but mild damage in fish collected from UZ. These histological alterations and the health risk indices disclosed the effects of effluents of chromite mining and the impact on the ecological balance which may result into health hazards to the local human population who are maintaining their livelihood by consuming these fish as protein source.

Deposition of Potentially Toxic Metals in the Soil from Surrounding Cement Plants in a Karst Area of Southeastern Brazil

Cement factories are the main sources of environmental pollutants among the different industrial activities, including soil contamination by potentially toxic metals. The karst region of Southeastern Brazil is known for the implementation of large cement producing facilities. This study aims to evaluate whether there is an increase in the concentration of PTM in the soil surrounding the cement plants and to estimate their harmfulness to both local human population and environment. In total, 18 soil samples were collected from the surroundings of three cement plants as well as four soil samples from areas outside the influence of cement plants and concentration of the following potentially toxic metals (PTM) were estimated: Cd, Pb, Co, Cu, Cr, Mn, Ni, and Zn. The results revealed that all PTM concentrations from cement plant surroundings were significantly higher than PTM concentrations from control areas and no PTM concentrations from CPS or CA soil samples exceeded national and global contamination thresholds. However, Igeo Index indicated low level soil contamination by Pb, Cu, and Cr, as well as high levels for Co. We could not verify significant non-carcinogenic risk to health for any soil sample, but carcinogenic risk analysis revealed different levels of carcinogenic risk among the sampled locations, for both adults and children. Our results indicate that exclusively evaluating the concentration of potentially toxic metals is not enough to verify the potential harmful effects of cement production for the surrounding population. Here we evidence that additional indices, based on both contamination indices and health risk assessments, should be considered for better evaluation of the impacts of cement production activity.

Potentially toxic metals in the petroleum waste contaminated soils lead to human and ecological risks in Potwar and Kohat Plateau, Pakistan: Application of multistatistical approaches

Until recently scant attention has been paid to assess the total concentration of potentially toxic metals (PTMs) in petroleum waste are more likely because once they enter in to the soils may become a source of contamination. This study investigated the concentrations of PTMs in soils of Potwar and Kohat plateau, Pakistan. Remarkable increase in the total concentrations of Cd, Cu, Mn, Ni and Pb were found in petroleum waste contaminated soils. Multi-statistical techniques such as Pearson correlation matrix analysis (PCMA) and principal component analysis (PCA) were used to establish a hypothesis that petroleum waste is a source of PTMs contamination in soils. The result of PCMA and PCA techniques confirmed that among PTMs, Cd followed by Mn was greatly whereas Zn and Pb were least affected by petroleum waste contamination in the soils. Ecological risk assessment was evaluated via contamination factor (CF), pollution load index (PLI), Nemerow integrated pollution index (NIPI), and ecological risk indexes (ERI). CF showed moderate contamination of soil with PTMs whereas Cd was found to cause high ecological risk to the surrounding environment. Enrichment factor (EF) was found in decreasing order as: Cd>Mn>Co>Cr>Cu>Ni> Zn> and Pb. Human health risk assessment in term of chronic daily intake (CDIingestion, CDIdermal, CDIinhalation), hazard quotient (HQingestion, HQdermal, HQinhalation), hazard index (HI) and total hazard risk index (THRI) of PTMs were evaluated for both child and adult indicating non-carcinogenic risk (NCR) value ≥1.

Bioaccessibility of potentially toxic metals in soil, sediments and tailings from a north Africa phosphate-mining area: Insight into human health risk assessment

The risk assessment of phosphate mining/processing industrial activities on the environment and human health is crucial to properly manage and minimize the risks over time. In this work, we studied the inhalation and dermal bioaccessibility of potentially toxic metals (PTM) in different particle-size fractions of urban soil, sediments and tailings from Gafsa-Metlaoui phosphate mining area, to assess afterwards the non-carcinogenic (NCR) and carcinogenic (CR) risks for the health of local citizens and workers constantly exposed to airborne particulate matter (PM) originating from these sources of contamination. Samples were separated in particle-size fractions by centrifugation and consecutive cycles of sedimentation and decanting. The pseudo-total concentrations and bioaccessible fractions of PTM were extracted by aqua regia and in vitro bioaccessibility tests, respectively. Both sediments and tailings showed higher-than-background concentrations of PTM (mainly Cd, Zn and Cr), with a tendency to accumulate these metals in fine particles (<10 μm). In urban soil, only Cd was above the background concentration. The bioaccessibility of PTM via inhalation was significantly higher in artificial lysosomal fluid (ALF) than in simulated epithelial lung fluid (SELF): basically, Cd was the most bioaccessible metal (relative bioaccessibility up to 80%), followed by the medium-to-high bioaccessible Zn (47%), Pb (46%) and Cu (39%), and the least bioaccessible Cr (16%). In synthetic skin surface liquid (NIHS 96-10), only Cd was bioaccessible at worrying extent (20–44%). On the basis of US.EPA risk assessment, the exposure to PTM bioaccessible fractions or pseudo-total concentrations would not cause serious NCR and CR risks for human health. Significant health risks (Hazard Index >1 and CR > 10−4), especially for children, can occur if ingestion route is also considered. The findings underline the need for adequate protection of contaminated soil, sediments and mine tailings laying nearby urban agglomerates, to reduce the health risks for inhabitants and workers of Gafsa-Metlaoui mining area.

Contamination of soil with potentially toxic metals and their bioaccumulation in wheat and associated health risk.

The present study was conducted to investigate the concentrations of potential toxic metals (PTMs) in agricultural soil (n = 25) and their bioaccumulation in wheat crop (n = 25) collected from alongside the Kurram River, Pakistan. The highest concentrations of Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn in soil samples were 0.16, 19.5, 14.7, 46.5, 13.5, 14.5, 14.0, and 19.7mgkg-1, respectively. In the edible tissues of cultivated wheat crop, the highest concentrations of Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn were 0.15, 10.00, 8.75, 22.25, 11.00, 11.25, 10.50, and 7.50mgkg-1, respectively. The selected PTM concentrations in soil samples were observed within their respective permissible limits set by the Food and Agriculture Organization (FAO) and State Environmental Protection Administration (SEPA) China, while in wheat crops, the Cr and Pb concentrations were above the permissible limits of both FAO and SEPA China. The results showed that the orders of PTMs were Fe > Zn > Cr > Cu > Ni > Pb > Mn in soil and Fe > Ni > Mn > Pb > Cr > Cu > Zn in wheat. The highest PTM concentrations were reported in the sample collected near dumping sites. The results of different soil pollution indices including geo-accumulation index (Igeo), contamination factor (CF), and enrichment factor (EF) indicated that the soil of the study area was moderately to severely contaminated. The ADI values of wheat crops were less than 1, while the HQ varied among different PTMs with the highest value of 2.118 for Pb, and the lowest for Zn (0.007). The results indicated that anthropogenic intervention has made a substantial contribution to soil contamination with PTMs and subsequent uptake by wheat, which may exert potential human health risk.

The Link between Antimicrobial Resistance and the Content of Potentially Toxic Metals in Soil and Fertilising Products

Potentially toxic metals (PTM), along with PTM-resistant bacteria and PTM-resistance genes may be introduced to soil and water through sewage systems, direct excretion, land application of biosolids (organic matter recycled from sewage, especially for use in agriculture) or animal manures as fertilisers, and irrigation with wastewater or treated effluents.&#x0D; The Norwegian Food Safety Authority (NFSA) asked the Norwegian Scientific Committee for Food Safety (Vitenskapskomiteen for mattrygghet, VKM) for an assessment of the link between antimicrobial resistance (AMR) and potentially toxic metals (PTM) in soil and fertilising products.&#x0D; The NFSA would like VKM to give an opinion on the following question related to the influence of potentially toxic metals on antimicrobial resistance:&#x0D; &#x0D; Can the content of arsenic (As), cadmium (Cd), chromium (CrIII + CrVI), copper (Cu), lead (Pb), mercury (Hg), nickel (Ni), and zinc (Zn) in soil and fertilising products that are relevant for Norway play a role in the development, spreading, and persistence of bacterial resistance to these elements, as well as cross or co-resistance to antimicrobial agents?&#x0D; &#x0D; VKM appointed a working group, consisting of two members of the Panel on Biological Hazards, to prepare a draft Opinion document and answer the questions. The Panel on Biological Hazards has reviewed and revised the draft prepared by the working group and approved the Opinion document “The link between antimicrobial resistance and the content of potentially toxic metals in soil and fertilising products”.&#x0D; In this report we assess the following PTM: arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), mercury (Hg), lead (Pb), and zinc (Zn), because of their possible presence in fertilisers and their potential to induce AMR in bacteria.&#x0D; This assessment is based on internationally published data. There is no systematic monitoring for toxic metals in soils in Norway, and the levels are expected to be highly variable depending on the input sources, previous and current agricultural practices, and the characteristics of the soil. Data on PTM in fertilising products added to soil are also fragmented and limited. Fertilising materials, in the form of sewage sludge or livestock manure, will add toxic metals to the existing levels in soil, and in areas of intensive agriculture, the levels will be expected to be highest. The additive effect of toxic metals in fertilising materials must be assessed from a long-term perspective, as these metals accumulate in the environment.&#x0D; Development of AMR can be partly regarded as a dose- and time-dependant response to exposure to different drivers for resistance. There is an indication that the presence of potentially toxic metals is a driver for development of AMR in exposed bacteria, but the dose and time exposure most likely to cause this effect is not known. Investigation of PTM-driven co-selection of AMR in environments impacted by agriculture and aquaculture should focus especially on Cu and Zn, which are added to animal feed, and on Cd because of its high concentration, in comparison with other PTM, in inorganic fertilising products. The naturally occurring background resistance in environmental bacteria complicates the estimation of the effect of PTM exposure on development of resistance. In addition, it is difficult to distinguish between the natural resistome and an elevated abundance of AMR in environmental samples.&#x0D; Spreading of resistance towards the PTM evaluated in this assessment involves cross- and co-resistance to antimicrobial agents used in prophylaxis and therapy in animals and people. Most important are those cases where toxic metal resistance is coupled to resistance towards highly important and critically important antibiotics. This has been described in some of the published articles included in this assessment. We do not fully understand the mechanisms behind persistence of AMR, and removing drivers for development and spread of resistance may result in a decrease in the levels of resistance, but not necessarily full disappearance.&#x0D; There is lack of knowledge regarding links between the level and concentration of PTM in fertilising products and soil and development of resistance in bacteria. Data regarding the routes and frequencies of transmission of AMR from bacteria of environmental origin to bacteria of animal and human origin were lacking in the published articles reviewed here. Due to the lack of such data, it is difficult to estimate the probability of development, transmission, and persistence of PTM resistance in the Norwegian environment. More research is needed to explain the relationship between development of resistance against potential toxic metals and resistance toward antimicrobial agents in bacteria.

Repeated extreme particulate matter episodes due to fireworks in Iceland and stakeholders’ response

Abstract Extreme pollution associated with residential firework celebrations is recognized as an important health and environmental issue. Despite this knowledge, consumer fireworks continue to be allowed in many countries around the world. This paper explores the physical and societal factors contributing to extreme recreational firework pollution, as well as stakeholders' perspectives on the resultant pollution and possible mitigation. Metropolitan Reykjavik (217 000 inhabitants) is taken as an example of an affluent, well informed community with a relatively recent history of fireworks displays. Largely non-regulated public access to fireworks has resulted in exceedance of the European air quality standard of PM10 (50 μg/m3), and hazardous hourly concentration (>500 μg/m3) every other year. In the second hour of New Year's Day (NYD) 2018, hourly particulate matter records, 4042 μg/m3 PM10 and 3014 μg/m3 PM2.5, were set in a residential, suburban area. Concentrations of potential toxic metals increased by a factor of 104 (Cu), 96 (Sr), 27 (Ba) during the celebrations compared to the preceding days. The reasons why these high pollution episodes continue to occur, based on stakeholders' interviews, are traced back to a series of societal and regulatory hurdles: (1) Conflicting interests at governmental, municipal and entrepreneurial levels because fireworks are an entertaining spectacle for locals and tourists and a major fundraiser for not-for-profit organizations (NPOs), and yet pose an unacceptable public burden in terms of air pollution. (2) The lawful public access to fireworks severely limits stakeholder involvement and air quality mitigation actions. (3) Implementation of fireworks policy is dispersed among multiple stakeholders. These factors promote stakeholder passiveness towards pollution mitigation: Continuing public awareness campaigns with the goal of slowly weaning the public off fireworks were favored over restricting public use to fireworks. Future opportunities lie in holistic policy making, using the United Nations Sustainable Development Goals as a roadmap; and in clarifying the risk of extreme particulate matter episodes in the relevant regulations, e.g. by accounting for the level of exceedances (concentration value divided by ambient air quality standard), and the nature of the particles (size, morphology, chemical composition).

Potentially toxic metal contamination and microbial community analysis in an abandoned Pb and Zn mining waste deposit

Bioindicators have been widely used to assess the contamination of lead/zinc (Pb/Zn) in smelter areas, mining waste disposal areas and in areas containing slags from Pb ore smelting. In this context, the analysis involving microorganisms has gained prominence as a complementary tool in studies aimed at assessing contaminated sites. Therefore, the objective of this study was to assess the contamination of Pb, Zn and cadmium (Cd) in an area where a PbZn smelter operated, using the integration of geochemical and microbial data. The experimental analysis was conducted to characterize the soil collected at three different sites (samples NS, EW and EP). The analysis conducted was physicochemical, metal concentration, metal speciation and analysis of the microbial community through high-throughput sequencing technique. Through the results it was observed that the high concentrations of metals altered the bacterial community present in the soil. Differences were noted between the microbial communities according to the sampling site, especially in sample EP, collected at the margin of the dirt road, which presented higher metal concentrations and microbial diversity. The main phyla detected in the samples were: Proteobacteria, Bacteroidetes and Acidobacteria. Bacteria tolerant to the presence of potentially toxic metals (PTM), such as Rhodoplanes, Kaistobacter, Sphingomonas and Flavisolibacter were identified in the analyzed samples. The phylogenetic groups identified in the study area are similar to those obtained in other studies in metal contaminated areas. The differences between the bacterial communities in each sample indicate that the concentration of PTM may have influenced the microbial community in the soil. Thus, it is noted the importance of the integration of geochemical and microbial data to evaluate the impact of the improper disposal of high PTM concentrated slags in natural soils.

Mapping human health risk from exposure to potential toxic metal contamination in groundwater of Lower Dir, Pakistan: Application of multivariate and geographical information system

The study aimed to assess the physicochemical parameters (pH, electrical conductivity (EC), total dissolve solid (TDS), oxidation reduction potential (ORP), Temperature) and potential toxic metals (PTMs), including Ni, Mn, Cr, Cu, Cd, Pb, Co, Fe and Zn in the groundwater of Lower Dir, Pakistan. Furthermore, the pollution sources and spatial distribution pattern of PTMs were also investigated via principal component analysis (PCA) and geographic information system (GIS) application to understand the changing behaviors of PTMs in groundwater. The average concentrations of physicochemical parameters such as pH, EC, TDS, ORP and Temperature were 7.1, 418 μS/cm, 251 mg/L, 193 mV and 25.7 ○C, while the concentrations of PTMs; Ni, Mn, Cr, Cu, Cd, Pb, Co, Fe and Zn were 0.25, 0.34, 0.09, 0.29, 0.10, 0.08, 0.10, 0.83 and 0.25 mg/L, respectively. Among the selected metals, Mn, Cr, Cd, Pb, Co and Fe were exceeded the WHO guidelines and their percentage contribution were 43%, 57%, 45%, 70%, 70% and 62%, respectively. The increasing order of PTMs were; Pb > Co > Fe > Cr > Cd > Mn > Cu > Ni > Zn in the study area. PCA represented three significant factors, which explained 76% variability in the groundwater. Whereas, clustering analysis (CA) grouped groundwater into three distinct clusters less polluted (C1), moderate polluted (C2) and highly polluted (C3). Human health risk assessment was carried out to check the suitability of groundwater for drinking and domestic uses. The HQ and HRIs values of Cd were >1, suggested that the groundwater sources are unfit for drinking and domestic purposes and may be caused potential health risk after long term ingestion.

Assessment of Human Health Risk of Potential Toxic Metals in Herbal Concoction Teas Commonly Consumed in Nigeria

Concentrations of potential toxic metals (Pb, Cr, Cu, Zn, Ni, Co, As, Fe and Mn) were determined in herbal concoction teas commonly consumed in Nigeria using Atomic Absorption Spectrophotometry. Results revealed that Fe had the highest concentration with a mean value of 13.136 ± 0.195 µg/g, while As had the least mean concentration (0.043 ± 0.006 µg/g). Pollution index (PI) result indicated that the teas were contaminated with Cu (PI value > 1) while it was clear of contamination by the other investigated metals. Cluster analysis showed close inter-element relationships between the investigated metals, indicating similar chemical properties and/or genetic origin. Correlation matrix showed that positive and significant correlations existed between between Zn/Cr, Ni/Cr, Co/Cr, Fe/Cu, Mn/Cu, Ni/Zn, Co/Zn, Co/Ni and Mn/Fe, indicating chemical affinity. Estimated daily intake, target hazard quotient and cancer risk showed that there was no health risk associated with the consumption of the herbal concoction teas. Relative risk indicated that the highest concern is from the levels of Co in the teas. The study concluded that consumption of the teas may not pose risk to human health at the current levels of the metals, but should be consumed moderately to prevent bioaccumulation of the metals.

Pyrolysis of contaminated wheat straw to stabilize toxic metals in biochar but recycle the extract for agricultural use

Minimizing potential environmental risks of toxic metals is a prerequisite for recycling crop straw from contaminated farmlands. In this study, feedstocks of wheat straw were collected from paddy fields with low and high level of metal contamination and pyrolysed at temperature of 350 °C and of 550 °C, respectively. The produced biochars were subsequently extracted with hot water and potassium hydroxide solution. Contents of potentially toxic metals (PTEs), polycyclic aromatic hydrocarbons (PAHs) and mineral nutrients were analyzed both of the biochars and their extracts. To test the effect of the biochar extracts on plant growth and quality, a pot experiment was carried out with foliar amendment to Chinese cabbage. The results showed that contents of nutrients, PTEs and PAHs of both the biochars and their extracts differed significantly both between feedstocks and between pyrolysis temperatures. Total concentrations of PTEs and PAHs of the biochars were well under the recommended quality limits with their negligible presence in the biochar extracts. The pot experiment revealed a very significant promotion for cabbage yield and quality by the extracts of biochar pyrolysed at 350 °C, regardless of the feedstock. Thus, pyrolysing crop straw from metal contaminated fields at 350 °C could be an option to stabilize toxic metals in biochar as soil amendment but to recycle the biochar extract as foliar fertilizer to off-site crop production. Therefore, a viable mechanism is urged to develop in China where direct crop residue return has been state-funded under a policy of strict ban of straw burning.

Acidic leaching of potentially toxic metals cadmium, cobalt, chromium, copper, nickel, lead, and zinc from two Zn smelting slag materials incubated in an acidic soil

A column leaching study, coupled with acid deposition simulation, was conducted to investigate the leaching of potentially toxic metals (PTM) from zinc smelting slag materials (SSM) after being incubated in an acid Alfisol for 120 days at room temperature. Two SSMs (SSM-A: acidic, 10 yrs exposure with moderate high PTM concentrations versus SSM-B: alkaline, 2 yrs exposure with extremely high PTM concentrations), were used for the incubation at 0.5, 1, 2.5, 5 wt% amendment ratios in triplicate. Five leaching events were conducted at day 1, 3, 7, 14, and 28, and the leaching of PTMs mainly occurred in the first three leaching events, with the highest PTM concentrations in leachate measured from 5 wt% SSM amendments. After leaching, 2.5, 12, 5.5, 14, 11, and 9 wt% of M3 extractable Pb, Zn, Cd, Co, Cr, and Ni could be released from 5 wt% SSM-A amended soils, being respectively 25, 12, 4, 2, 2, and 2 times more than those from 5 wt% SSM-B amended soils. In the leachates, the concentrations of PTMs were mostly affected by leachant pH and were closely correlated to the concentrations of Fe, Al, Ca, Mg and P with Cd, Pb, and Zn showing the most environmental concern. Visual MINTEQ 3.1 modeling suggested metallic ions and sulfate forms as the common chemical species of PTMs in the leachates; whereas, organic bound species showed importance for Cd, Pb, Cu, and Ni, and CdCl+ was observed for Cd. Aluminum hydroxy, phosphate, and sulfate minerals prevailed as the saturated minerals, followed by chloropyromorphite (Pb5(PO4)3Cl) and plumbogummite (PbAl3(PO4)2(OH)5·H2O) in the leachates. This study suggested that incubation of SSMs in acidic soil for a long term can enhance the release of PTMs as the forms of metallic ions and sulfate when subjected to acid deposition leaching.

Statistical analyses and risk assessment of potentially toxic metals (PTMS) in children’s toys

Chemical exposure of children, especially from toys, is an engineering concern. The concentration and availability of potentially toxic metals (PTM) in children’s toys were determined to assess the risk that these metals pose to children. Samples of 25 toys imported from China to Nigeria were purchased. Ternary acid digestion, followed by Atomic Absorption Spectrophotometry, was used to determine the concentration of PTM in the sample. Simulations of the saline and stomach acid extraction conditions were performed to determine the concentrations of PTM that could leach out from the toys during children’s mouthing behaviours (available PTM), including chewing, sucking and swallowing. The total concentrations of PTM in the toys ranged from 3.55–40.7, 3.21–38.2, 9.78–159, 3.55–11.2, and 36.1–106mg/kg for Cd, Cr, Cu, and Pb, respectively. Availability studies showed concentrations ranging from 2.60–5.60mg/kg for Pb, 0.53–2.03mg/kg for Cd and 0.15–2.88mg/kg for Ni after saline extraction, and the concentrations after stomach acid extractions ranged from 3.33–7.10mg/kg, 1.15–3.15mg/kg and 1.33–1.81mg/kg for Pb, Cd and Ni, respectively. Statistical analysis showed a positive correlation between the total concentration of PTM and toys made from PVC materials. The risk assessment study showed that Cd posed the highest risk, with a hazard index (HI) as high as 4.50 for saline extraction. The study revealed that more precaution is needed during the manufacture of children’s toys.

Biochar application to a contaminated soil reduces the availability and plant uptake of zinc, lead and cadmium

Heavy metals in soil are naturally occurring but may be enhanced by anthropogenic activities such as mining. Bio-accumulation of heavy metals in the food chain, following their uptake to plants can increase the ecotoxicological risks associated with remediation of contaminated soils using plants. In the current experiment sugar cane straw-derived biochar (BC), produced at 700 °C, was applied to a heavy metal contaminated mine soil at 1.5%, 3.0% and 5.0% (w/w). Jack bean (Canavalia ensiformis) and Mucuna aterrima were grown in pots containing soil and biochar mixtures, and control pots without biochar. Pore water was sampled from each pot to confirm the effects of biochar on metal solubility, whilst soils were analyzed by DTPA extraction to confirm available metal concentrations. Leaves were sampled for SEM analysis to detect possible morphological and anatomical changes. The application of BC decreased the available concentrations of Cd, Pb and Zn in 56, 50 and 54% respectively, in the mine contaminated soil leading to a consistent reduction in the concentration of Zn in the pore water (1st collect: 99 to 39 μg L−1, 2nd: 97 to 57 μg L−1 and 3rd: 71 to 12 μg L−1). The application of BC reduced the uptake of Cd, Pb and Zn by plants with the jack bean translocating high proportions of metals (especially Cd) to shoots. Metals were also taken up by Mucuna aterrima but translocation to shoot was more limited than for jack bean. There were no differences in the internal structures of leaves observed by scanning electron microscopy. This study indicates that biochar application during mine soil remediation reduce plant concentrations of potential toxic metals.

Multivariate analysis of potentially toxic metals in sediments of a tropical coastal lagoon

Surface sediments collected from the Lagos Lagoon, Nigeria, and three adjoining rivers were analysed for their physicochemical properties and pseudo-total concentration of the potentially toxic metals (PTM) Cd, Cr, Cu, Pb and Zn. The concentration of the PTM varied seasonally and spatially. Odo-Iyaalaro was observed to be the most polluted river, with highest concentrations of 42.1mgkg(-1), 102mgkg(-1), 185mgkg(-1), 154mgkg(-1) and 1040mgkg(-1) of Cd, Cr, Cu, Pb and Zn, respectively, while Ibeshe River was the least contaminated, apart from a site affected by Cu from the textile industry. Some of the sediments were found to be above the consensus-based probable effect concentrations and Dutch sediment guideline for metals. Overall metal concentrations were similar to those reported for other tropical lagoon and estuarine systems affected by anthropogenic inputs as a result of rapid urbanisation. Due to the large number of samples, principal component analysis was used to examine relationships within the data set. Generally, sediments collected during the dry season were observed to have higher concentration of PTM than those collected during the rainy season. This means that PTM could accumulate over a prolonged period and then be released relatively rapidly, on an annual basis, into tropical lagoon systems.

Micromorphological and Chemical Approaches to Understand Changes in Ecological Functions of Metal-Impacted Soils under Various Land Uses

We investigated the changes in faunal activities as measures of the ecological functions of soils impacted by potentially toxic metals (PTMs) under urban, industrial, agricultural, and natural uses. Concentrations and distributions of Zn, Cd, Pb, Cu, Mn, and Fe were estimated by sequential chemical extractions, while relicts and present faunal activities were studied by micromorphological analyses. Urban and natural lands were contaminated with Pb, Cd, and Zn. Microarthropods and fungi are observed to be active in the litter decomposition in natural, agricultural and urban lands which indicates that total concentration of PTMs in soils is not a good indicator to evaluate the limitations of PTMs to fauna activity. Metals immobilization on carbonates and Fe/Mn oxides, and fertilizations reduced the negative effects of metals on faunal activity. Micromorphological analyses showed the impacts of metal on soil ecological functions in industrial site, where the surface soils are devoid of any evidence of faunal activity; likely due to high proportion of Pb and Zn in organic components. Therefore, the impacts of metals in soil fauna activities, hence ecological functions of soils, are best evaluated by the knowledge of metal partitioning on solid phases in combination with observations of fauna activities using micromorphological techniques.