Biochar is frequently applied for the reduction of mercury (Hg) migration in soil; however, most of the studies only focused on the adsorption capacity evaluation of fresh biochar. We investigated the Hg adsorption capacities of biochar prepared from wheat straw, corn straw, and sunflower seed shells. Biochar aging was simulated via natural aging, high-temperature aging, and freeze-thaw aging. The adsorption capacities of all the aged biochar were increased, and wheat straw biochar and seed shells biochar treated with high-temperature aging (wBC-Ha500 and sBC-Ha600) and corn straw biochar treated with freeze-thaw aging (cBC-Fta500) showed an observable improvement on the equilibrium adsorption amounts. The kinetics of the fresh biochar samples fitted the pseudo-first-order kinetic model and the pseudo-second-order kinetic model, while the kinetics of the aged biochar samples fitted the pseudo-second-order kinetic model. Biochar adsorption capacity increased with higher initial concentrations and increasing temperatures. Elemental analysis, Fourier-transform infrared spectroscopy (FT-IR) spectra, cation-exchange capacity (CEC), surface area (SA), zeta potential, and X-ray photoelectron spectroscopy (XPS) showed that the aging mechanism consisted of hydroxylation and carboxylation caused by the functional groups on the biochar surface. According to the different climatic zones in China, wheat straw biochar and seed shell biochar are suitable for the tropical zone and the subtropical zone, while corn straw biochar is more suitable for the cold and the mid-temperate zones.

Background. Harmful wastes and other dangerous industrial by-products constitute major sources of environmental pollutants in Nigeria. Industrial pollutants discharged into the environment contain organic and inorganic pollutants in dissolved, suspended and insoluble forms. Fishes are known for their innate potential to bioaccumulate heavy metals in their muscles and various organs. Objectives. The present study aimed to assess the bioaccumulation status of heavy metals in selected organs and tissues of African catfish in Asa River, Ilorin, Kwara State, Nigeria. Methods. Three sampling points (A (upstream), B (point of discharge) and C (downstream)) were selected in relation to industrial effluents that enter the river. African catfish were randomly harvested from each site using fishing nets at the three sampling points. The samples were digested and subjected to atomic absorption spectrophotometric analysis. Statistical analysis of data was carried out using the Statistical Package for the Social Sciences (SPSS) version 20 and two-way analysis of variance (ANOVA) to compare data among sites and organs. Results. The present study found that the bioaccumulation level of heavy metals in selected organs and tissues of African catfish in Asa River, Ilorin, Kwara State, Nigeria was very high and the level of accumulation of heavy metals increased downstream. Accumulations were much higher during the dry season (especially in the month of February) and relatively low during the peak of the rainy season. Conclusions. Heavy metals at elevated levels in the aquatic environment can accumulate in fish tissues and organ, and therefore fish from the Asa River are not fit for human consumption. Competing Interests. The authors declare no competing financial interests.

Background. Recent studies have explored the potential for using biochar as a soil amendment in agriculture. However, it can also be used as a gentle remediation option for contaminant reduction. Biochar is a by-product obtained from the pyrolysis of biomass (organic matter). It is known for its long-lasting chemical properties, wide surface area values, and carbon-richness, which make it an efficient method for the immobilization of organic and inorganic contaminants such as heavy metals. Objective. The aim of the present study was to analyze the efficiency of biochar, obtained from the gasification of corncob, for the immobilization of lead in contaminated soils. Methods. In the present study, biochar from corncob was used as an amendment for soil contaminated with lead (extracted from the municipality of Malambo, Colombia) in order to estimate its ability to immobilize leaching lead. A comparison laboratory test applied a modified biochar produced with a 10% hydrogen peroxide chemical treatment. In addition, a pot experiment was done with both biochar by sowing seeds of Pennisetum clandestinum for 33 days. During this period, plant growth was measured for the different amendments of biochar concentrations. Results. Laboratory tests indicated that unmodified biochar obtained a maximum retention of 61.46% of lead, while the modified biochar obtained only 44.53% retention. In the pot experiments, the modified biochar indicated high germination and growth of seeds (up to 89.8%). Conclusions. Although the lead immobilization in soil was positive for both cases, the use of soil with high concentrations of lead (167.62 g/kg) does not indicate biochar's effectiveness for purposes of comparison with the current United States Environmental Protection Agency (USEPA) limit value (400 ppm for bare soil in urban play areas). Therefore, further studies are recommended using soil with lower lead concentration levels. Competing Interests. The authors declare no competing financial interests. One author is an employee of Pure Earth.

Background. Electronic waste (e-waste) contains both valuable and hazardous materials. E-waste scavengers specialize in the collection and crude recycling of waste electronics to retrieve valuable metals, which are then sold. These activities provide an income for scavengers, but also expose them to toxic heavy metals such as lead (Pb) and copper (Cu). Objectives. The aim of the present study was to investigate the level of awareness and concentrations of heavy metals (Pb, Cu, zinc (Zn) and manganese (Mn)) in the blood levels of e-waste scavengers at Jakande dumpsite, Alaba International Market, Lagos, Nigeria. Methods. Material and data were collected by empirical survey with the use of a questionnaire to obtain information from e-waste scavengers. Blood samples of the scavengers in the present study (30 adult males exposed to recycling processes) were collected and concentrations of heavy metals were determined through acid digestion and the use of an atomic absorption spectrophotometer (AGILENT 55B AA, 2010). Results. The geometric means of blood levels of Pb, Cu, Zn and Mn were 11.0, 33.85, 126.15 and 19.38 μg / dL, respectively. High concentrations of Pb and Mn (11.0 and 19.38 μg / dL) were found in the blood samples, while Zn and Cu (126.15 and 33.85 μg / dL) showed low concentrations. The maximum blood level of lead (BPb) (24.0 μg / dL) was extremely high compared to the maximum BPb of occupationally exposed males. Statistical analysis of the questionnaires showed that all of the respondents were male, and more than half (56.7%) were between 21–30 years of age and had been involved in recycling of e-waste for 1–5 years. The results showed that 83% of the respondents were aware that hazardous fractions in e-waste require special treatment, while 76.7% were aware of the possible negative impact on their health. Conclusions. Lack of education, poverty and lack of effective enforcement of e-waste management and regulations are the major contributors to the current situation and thus scavengers carry on with their activities unhindered. The authors recommend the use of protective clothing, sensitization visits and awareness campaigns on the safe disposal of hazardous components. Participant consent. Obtained Ethics Approval. The study was approved by the ethics committee of the Lagos State University Teaching Hospital, Ikeja Lagos. Competing Interests. The authors declare no competing financial interests.

Background. Fluted pumpkin (Telfairia occidentalis) and amaranth (Amaranthus spp.) are common leafy vegetables produced and consumed in southwestern Nigeria. These vegetables attract insect pests which are controlled by pesticides that may have adverse impacts on human health. Objectives. To determine the levels of dichlorodiphenyltrichloroethane (DDT) and hexachlorocyclohexane (HCH) pesticide residues in the two vegetables and evaluate the potential health risks associated with their consumption. Methods. The pesticide residue levels were quantitatively and qualitatively determined using a gas chromatograph coupled with electron capture detector. Health risk assessment were performed using estimated average daily intake and hazard indices for two weight categories: children (16.7 kg) and adults (60 kg). Results. The results showed that delta-HCH, DDT and methoxychlor were predominantly detected in the two vegetables from both farms and markets. In amaranth, the mean concentration of methoxychlor, DDT and delta-HCH were 4.590 ± 2.774 mg/kg (dry weight (dw)), 0.757 ± 0.457 mg/kg (dw) and 0.577 ± 0.390 mg/kg (dw), respectively, while fluted pumpkin levels were 6.223 ± 2.489 mg/kg dw (methoxychlor), 0.504 ± 0.056 mg/kg dw (delta-HCH) and 0.486 ± 0.123 mg/kg dw (DDT). The levels of HCH and DDT residues were generally above the United Kingdom/European Commission maximum residue limit. The analysis of health risk estimates for non-carcinogenic risk revealed that for both vegetables, the hazard quotient for p, p′ DDT and methoxychlor was >1 for both children and adults. The health risk estimates for carcinogenic risk revealed that hazard indices values were >1 for children for both vegetables and alpha-HCH had a hazard index >1 for adults for amaranth. This means the residue exceeds acceptable standard and present potential risk to consumers of these vegetables. Conclusions. The results obtained from the present study indicate that consumption of amaranth contaminated with alpha-HCH could pose a carcinogenic risk for adult consumers. The consumption of the two vegetables could pose both non-carcinogenic and carcinogenic health risks to children and adults. Therefore, there is need for strict enforcement of regulations on pesticide usage to minimize human health risks. Competing Interests. The authors declare no competing financial interests.

Background. Acute widespread lead poisoning took place in Zamfara State, Nigeria in 2010. Over 735 children were reported dead and thousands sickened by the neurotoxin. The source was traced to artisanal gold mining and processing in the villages. An immediate medical response protocol was developed to provide oral chelation therapy to the vulnerable population. In order not to compromise the efficacy of the chelation therapy, immediate remediation of the affected villages was carried out. An over 95% reduction in soil lead levels was reported immediately after the remediation exercise. Objectives. The aim of the present study was to perform a general audit of soil lead concentrations, conducted between June and July 2013 in Dareta village (one of the most affected villages), to evaluate the soil pollution status of the village three years after the remediation exercise. Methods. Soil samples were collected from residential compounds, cultivated farmlands and other common areas. Lead contents of the samples were determined using atomic absorption spectrophotometer (Shimadzu, model AA-6800, Japan) after wet digestion. Speciation of lead in soil was done following standard analytical methods. Results. Mean soil lead concentrations for residential areas were 1029.42±98.50 mg/kg, 1523.99±201.00 mg/kg, 1404.57±141.00 mg/kg and 6724.68±84.00 mg/kg for residential compounds, market square, old grinding mills and new grinding mills, respectively. The concentrations exceeded both the Dutch target and intervention values and US Environmental Protection Agency limit for soil lead levels in residential areas. Based on the index of geo-accumulation, the ranking of intensity of lead (Pb) pollution of Dareta soils ranged from strongly polluted to extremely polluted, indicating they pose a range of moderate to very high potential ecological risk to the other components of the environment. At the current rate of accumulation, by the year 2025, soil Pb levels of Dareta common areas are expected to exceed the pre-remediation levels associated with several deaths. Conclusions. Findings of this study indicate that the problem of lead poisoning is ongoing in Dareta village. Zamfara State authorities should address the challenge through sustained periodic assessment and cleanup of affected areas. Implementation of safer mining practices should be enforced immediately. Competing Interests. The authors declare no competing financial interests

Background. Mercury in dental amalgam is a hidden source of global mercury pollution, resulting from the illegal diversion of dental mercury into the artisanal and small-scale gold mining sector, to crematoria emissions from the deceased and sewage sludge that is sold to farmers. These significant mercury sources result in air, water, and food contamination that consequently have a negative impact on human health. Objectives. The aim of the present study was to investigate and report on all of the various pathways mercury in dental amalgam can enter the environment. Methods. The present study searched the electronic data bases of PubMed and Google Scholar. Peer reviewed journals and references of studies included for full-text review were examined for potentially relevant studies. Articles published between 2000 to 2018 were searched and specifically screened for articles that referenced “Dental Amalgam,” and the following key words in various combinations: “Minamata Convention on Mercury Treaty,” “Sewage Sludge,” “Cremation,” and “Artisanal and Small-Scale Gold Mining.” Data were included on the most populous countries of China, India, the United States, Brazil, and the European Union collectively. We also included data on cremation statistics and current global trends, looking at populations where cremation is a common practice, such as Japan and India. Discussion. Dental amalgam represents a significant, but understudied area of global mercury pollution that includes cremation, sewage sludge, burial, and small-scale gold mining. Conclusions. Mercury used in products and processes, including dental amalgams, is a global pollutant. Even after the last mercury dental amalgam is placed, its toxic legacy will continue for decades, because of its pervasive bioaccumulation in the environment. Government regulatory agencies should make it mandatory to utilize available technologies, not only in developing countries, but also in developed countries, to reduce mercury contamination. Competing Interests. The authors declare no competing financial interests.

Background. High arsenic levels in potable water are a threat to public health in India. About 85% of the water in India's rural areas comes from groundwater and roughly 27 million people are at risk of arsenic (As) contamination. Objectives. The present study was performed to examine the feasibility of providing an effective and affordable means for arsenic abatement in socio-economically poor and rural areas in India. This is the first report on the effectiveness of powder Nelumbo nucifera Gaertn (lotus) root biomass for As (III) eradication from aqueous solution. Methods. Batch experiments were conducted to determine the effects of various operating parameters, including pH, initial As (III) ion concentration, adsorbent dosages, and contact time for As (III) sorption onto lotus root. Discussion. The sorption efficiency of lotus root biomass for As (III) at pH 7 was found to be quantitative (96%) from 50 mg/L aqueous solution at a dose of 5gL−1. Capacity of the biosorbent for As (III) ion adsorption and the interaction between adsorbate with biosorbents were studied using Langmuir and Freundlich isotherm models. In the present study, the equilibrium parameter values ranged between 0 and 1, indicating that the adsorption of the As (III) ion onto lotus root biomass was favorable. Conclusions. Lotus root powder biomass was found to be an effective adsorbent for As (III) and could be used as an efficient, cost-effective and environmentally safe biosorbent for the sorption of arsenic from aqueous solutions. Competing Interests. The authors declare no competing financial interests.

Background. The enrichment of lead (Pb) in a rapidly expanding urban environment is largely caused by industrial and anthropogenic activities. However, very few studies have come from sub-Sahara Africa as a whole, in spite of the increased rate of population, industrialization and urbanization in this region. The city of Onitsha is the commercial heartland of southeast Nigeria. Objectives. To determine the concentration of Pb in soils and sediments in Onitsha and the surrounding area and to identify the possible sources of Pb content in the environmental media. Methods. One hundred and sixty-two (162) samples (120 top and subsoils, and 42 stream and side drain sediments) were collected from the city of Onitsha, Nigeria to determine Pb concentrations, identify the main sources of Pb in this region, and determine its fate in soil and sediments using Pb isotopes. Thirty (30) 15 g clay fractions of soil and sediment samples, and a sample each of galena (from the Lower Benue Trough), coal and soot from vehicle exhaust and battery cells were collected from the city and analyzed for lead isotopes (Pb204, Pb206, Pb207 and Pb208) using ultra-trace inductively coupled plasma emission spectrometry. Results. The distribution and concentration of Pb in the soil of Onitsha was observed to be influenced by land use patterns with very elevated concentrations of Pb observed for mechanic and metal workshop samples (1444.3, 1067.5, 1048.1, 1730.5 and 580.5 ppm); active waste dump samples (448.4 and 311.9 ppm); and farmland and garden samples (366.2 ppm). The concentration of Pb in the sediments also showed varying elevated concentrations across locations, ranging from 45.7–540.1 ppm. A comparison with the control samples revealed that the Pb concentrations measured in the environmental media were several folds higher than that of the control. The Pb isotope analysis indicated that most of the Pb in environmental media was anthropogenic in origin and had been predominantly contributed by unsustainable environmental practices such as indiscriminate waste dumps, hydrocarbonbased products emissions, by-products from mechanical workshops that have been haphazardly constructed in the city, and industrial plants located within urban areas. Conclusions. The relatively higher concentrations of Pb in soils and sediments were found to be influenced by land use, as also observed in the Pb isotope readings, which will, over time, adversely affect environmental media and biota. Competing Interests. The authors declare no competing financial interests.

Background. Brasilia, the capital of Brazil, currently has the largest dumpsite of the Americas at Estrutural, with over 30 million tons of waste accumulated. Recyclable waste collectors are a group of workers who, in addition to having a low socioeconomic status and residing in vulnerable areas, work sorting garbage in inadequate and unsanitary areas. This profession puts individuals at risk, resulting in death, mutilation, and disease for workers. Objectives. The aim of this study was to understand the effects of waste on recyclable collectors, along with their perceptions of associated risks. Methods. A qualitative study was conducted, using interviews with 34 participants at Estrutural. Results. Collectors were exposed to several hazards, including biological, physical, and more extreme hazards (e.g. being run over by waste trucks). Personal protective equipment was not adequately used, exposing recyclable collectors to injury. Accidents included cuts, burns, skin lesions, eyes lesions, and arm, leg, head, feet, and hand injuries and amputations. Often, homecare remedies and collected medical waste (e.g. pain killers) were used on these injuries instead of seeking out proper medical care. Conclusions. Recyclable collectors were aware of occupational hazards, but lacked education on the risks and consequences associated with exposure to medical hazards. Moreover, Brazil recently formally closed all dumpsites, complicating this issue. The findings of the present study confirm the need to address these hazards to provide a safe working environment for waste pickers. Participant Consent. Obtained Ethics Approval. This study was approved by the Research and Ethics Committee of the Health School of Brasília University under Opinion n. 1.517.670/2016. Competing Interests. The authors declare no competing financial interests.