Level Of Heavy Metal Pollution Research Articles

Monitoring the level of heavy metals pollution in automobile mechanic workshops using tree barks

The level of heavy metals at automobile mechanic workshops were monitored by examining tree barks of different species and influence of sampling heights on the metals level. This was with the aim of determining the suitability of using tree barks in monitoring the level of air pollution. Tree bark samples were collected at 2 and 4m heights from different automobile mechanic workshops around Ile-Ife metropolis and at control sites. The samples were transported to the laboratory, oven-dried at 60 ˚C to a constant weight; ground and analyzed for Pb, Cu, Cd, Fe and Zn using Atomic Absorption Spectrophotometer. Results showed that the concentration of Fe, Cu and Pb at the mechanic sites were significantly (p 0.05) between the sites. The correlation value of 0.94 was observed between Zn and Cd; 0.76 between Pb and Cd, and 0.50 between Zn and Pb. This study showed that different species have different affinities for air pollutants and that soil particles also acted as a source of heavy metals in our environment. Keywords: Atmospheric, Automobile, Pollutants, Soil particle, Trace metals, Tree barks

Laguna Verde Bay s sediments origin and its heavy metals content (Al, Fe, Cu, Mn, Pb, and Hg), Valparaiso, Chile

Laguna Verde Bay, a World Biosphere Reserve, seems to be barely uncontaminated due to its isolated geographical position (18 km south of Valparaiso, Chile) and low amount of anthropogenic activities. At its coastal border, there is a thermoelectric generator (using coal since 1939 and diesel since 2007 as fuel), a small village (≈10.000 inhabitants) and a local fishermen’s wharf. A freshwater creek flows into the beach, creating a small coastal pond that sporadically overflows into the bay. With the objective of estimating the origin of the Laguna Verde Bay surface sediments and its heavy metal pollution level, the content of Total Organic Matter (TOM), organic carbon to total nitrogen ratio (C:N ratio), stable carbon isotope ratio (δ 13C ), Al, Fe, Cu, Mn, Pb and Hg in samples collected in August 2015, were measured. According to the δ 13C values, the sediment origin was mostly terrestrial, with an allochthonous content greater than 50%. Since there is no legislation in Chile to establish the heavy metal concentrations for unpolluted marine sediments, a normalized metal enrichment factor (NEF) was computed to infer the contamination level. Despite the high Fe and Pb contents in the bay’s sediment at two stations (13.3 mg g -1 and 18.0 µg g -1 , respectively), the NEF values in the bay generally correspond to a low level of pollution.

Microbial Communities in Soils of Qingshuitang Industrial District in Zhuzhou

To study the effect of heavy metal pollution on microbial communities, microbial diversity and community structure of soils near Qingshuitang industrial district in Zhuzhou, China, were analyzed by Illumina high-throughput sequencing technology. In this study, the microbial diversity and community relative abundance decreased with increased heavy metal pollution level. Proteobacteria (49.56%) were the most abundant phylum in all samples, followed by Chloroflexi (13.07%) and Acidobacteria (8.77%). The microbial community structures of all samples were similar. The overlap of OTUs was 52.64%, and the structures of the abundant OTUs subcommunities were more similar than the rare OTUs community structures were. Heavy metals caused increases in Proteobacteria and Chloroflexi and decreases in Acidobacteria and Nitrospirae. According to Spearman's correlation, Proteobacteria was significantly negatively correlated with Cr, whereas Chloroflexi was positively correlated with Cr. Cd, Cu, Pb, and Zn were significantly negatively correlated with Nitrospirae. These results showed that heavy metal pollution is an important factor affecting the soil microbial structure in the soil of the Qingshuitang industrial district.

Heavy metal concentrations in sediments from Xingyun lake, southwestern China: implications for environmental changes and human activities

Environmental changes influenced by human activities were recorded in the sediment cores from Xingyun lake. Based on the 137Cs and 210Pb dating, multi-proxy records, enrichment factor (EF), and geoaccumulation index (Igeo) methods, the history of human–environment interactions in Xingyun lake catchment during the past 140 years was studied. The results showed that the total heavy metal pollution in Xingyun lake followed the decreasing order: the northwestern > the middle > the southwestern > the southern > the north easterly. These distributions were controlled by regional geochemical background values, pollution load, and the lake current driven by prevailing southwesterly winds. The total EF value of heavy metals followed the decreasing order: EF (Zn) > EF (Cr) > EF (Pb) > EF (Cd) > EF (Cu). The total Igeo value of heavy metals also followed the decreasing order: Igeo (Zn) > Igeo (Cr) > Igeo (Pb) > Igeo (Cd) > Igeo (Cu). Consequently, the total pollution level of heavy metals followed the decreasing order: Zn > Cr > Pb > Cd > Cu. Before 1910 AD, the natural erosion caused by climate changes was the key factor for the heavy metals accumulated. After 1910 AD, the heavy metal concentrations were mainly controlled by anthropogenic impacts, the dominant sources were from industrial pollution, agricultural pollution, mining, and organic degradation. Finally, the sedimentary evolution history of Xingyun lake can be divided into four stages, i.e., (1) natural evolution stage during 1862–1910 AD, (2) anthropogenic disturbance stage during 1910–1953 AD, (3) anthropogenic reconstruction stage during 1953–1984 AD, and (4) eutrophication stage after 1984 AD.

Heavy Metal Pollution Characteristics in the Modern Sedimentary Environment of Northern Jiaozhou Bay, China.

The particle size distribution characteristics of sediments and the concentrations of heavy metals in Jiaozhou Bay were investigated in this study. The average concentrations of Cu, Pb, Zn, Cr, Cd, Hg and As were 36.88, 29.60, 82.08, 77.48, 0.083, 0.048 and 11.00mg/kg, respectively. The heavy metal concentrations were highest in the eastern sediments, followed by those at the top of the bay, and the lowest concentrations were observed in the central region. Overall, a decreasing trend from the center of the bay to the periphery was observed. Additionally, the distribution of heavy metals in sediments was not completely controlled by sediment particle size. The degree of heavy metal contamination was evaluated using the geoaccumulation index and Hakanson's method. The results revealed that the level of heavy metal pollution in the sediments was relatively low and that the main pollution elements were Cu and Hg. In addition, the sediments are associated with various levels of potential ecological risk due to the high pollution levels of Hg and Cd.

A Review of Heavy Metal Contamination of Food Crops in Nigeria.

Heavy metal contamination of food crops is an issue of global concern that ultimately results in toxicity and diseases in humans and animals through consumption of contaminated soils and food crops. With a population of 182 million people, Nigeria is regarded as the most populous country in Africa. The people suffer environmental pollution from high levels of heavy metal accumulation in the environment and in food crops. Heavy metals have atomic densities higher than 4 g/cm3, and these include lead (Pb), cadmium (Cd), zinc (Zn), mercury (Hg), arsenic (As), silver (Ag), chromium (Cr), copper (Cu), iron (Fe), and platinum (Pt). The high level of environmental contamination by these metals is dangerous because their uptake by plants and subsequent accumulation in food crops consumed by humans and animals is deleterious to health. There are many known sources of harmful metals, including the earth, which releases them into food, air, and water, and anthropogenic activities, such as the application of fertilizer in agriculture, the use of pesticides and herbicides, and irrigation. Other sources are automobile emissions, paints, cigarette smoking, industries, and sewage and waste disposal. Evidence shows that vegetables and other food crops consumed in Nigeria are contaminated by heavy metals, and this is associated with adverse health issues, such as cancer, which is currently on the rise in Nigeria. It is therefore vital that communities with high levels of heavy metal pollution avoid eating large quantities of these food items. There is also the need for the monitoring of levels of these injurious elements in food crops.

Influence of age on the bioaccumulation of heavy metals in Apodemus sylvaticus at Merja Zerga lagoon, Morocco.

The influence of age and sex on the bioaccumulation of heavy metals in Apodemus sylvaticus was studied in Merja Zerga lagoon in northern Morocco. Five trace metal elements (Zn, Pb, Cr, Cu and Fe) were quantitatively analyzed by Varian AA 240 atomic absorption spectroscopy with graphite furnace in three organs (Liver, Kidney and Heart) from animals of different age and sex. The maximum metal level of the analyzed samples was recorded in adults and was limited to 46.62 μg/g for Pb and 35.1 μg/g for Cu, while it reached 22.69 μg/g, 7.59 μg/g and 6.78 μg/g for Cr, Zn and Fe, respectively. Highly significant differences were found for bioaccumulation of heavy metals according to animal ages and no significant differences were observed between the two sexes among the studied animals. Our results revealed also the existence of a strong correlation (r > 0.65) between the majority of biometric parameters and the trace element concentrations. In general, we found that age is a critical factor in estimating the level of heavy metal pollution. Other characteristics such as habitat, feeding habits and anti-predator behavior of the species need to be studied.

Nickel Exposure Has Complex Transgenerational Effects in a Butterfly.

Heavy metal pollution is a major problem in urban and industrial environments, and has a myriad of negative effects on animals. Quantifying the amount of population-level variation that exists for heavy metal tolerance and how plastic responses to heavy metals play out across generations are essential for understanding how animals respond to pollution. As an initial step toward studying transgenerational effects and population-level variation in concert, we brought cabbage white butterflies (Pieris rapae) from two populations-collected from St. Paul, MN, and Davis, CA-into common conditions and fed them a diet dosed with nickel. To measure transgenerational effects, we reared a second generation in a fully factorial design, within each population, to achieve all combinations of parent and offspring exposure to nickel or control diets. Across both generations, we quantified survival and other fitness-related traits, including development time, body size, and egg size and number. We found both population differences and complex transgenerational effects, including a positive effect of nickel on survival and development time in one of the populations. Overall, nickel exposure was stressful in one population, mainly after two generations of exposure, and had neutral or slightly positive effects on the other. We found no evidence for costs of mismatch between parental and offspring environments. While the reasons for the differences observed between the two populations are unclear, the variation in nickel tolerance observed in this species suggests that some organisms may be less affected by low levels of heavy metal pollution in urban and industrial areas than expected.

Effects of Highway-Related Pollutant on the Groundwater Quality of Turfy Swamps in the Changbai Mountain Area.

Transportation activities such as fuel consumption, vehicle wear and road deicing can detrimentally affect the groundwater quality of fragile roadside wetland environments including. Nineteen parameters (Cu, Pb, Zn, Cd, Cr, Ni, Hg, As, pH, TDS, Ca2+, Mg2+, Na+, K+, SO42−, Cl−, HCO3−, NO3− and F−) were determined in groundwater samples from turfy swamps impacted by highway traffic from Jiangyuan (JY), Longquan (LQ), and Huangsongdian (HSD). Our results indicate that the metals Cu, Pb, Zn, Cr, Cd, the ions Na+, K+ and Cl− in groundwater were negatively affected by highway transportation, and the maximum affected distance of these pollutants varied from 15 to 100 m. The content of most of these pollutants in roadside groundwater decreased exponentially with the distance from the highway, as did the heavy metal pollution index HPI and Cd. The values of HPI and Cd in these three sites ranged from 46.8 to 78.4 and −4.9 to −2.9, respectively. The low pollution levels of heavy metals are related to the strong adsorption capacity of turfy soil towards metals. In any case, road transport activities increased the Cu, Pb, Zn, Cr, Cd, Na+, K+ and Cl− content in roadside groundwater in turfy swamp. With the increase of highway operation time, it will inevitably have a great influence on the groundwater quality of these wetlands. Therefore, the long-term monitoring is necessary to protect the sustainable development of turfy swamp.

Pollution and Ecological Risk Assessment of Heavy Metals in Farmland Soils in Yanqi County, Xinjiang, Northwest China

A total of 50 farmland soil samples were collected from the Yanqi County, Xinjiang, China, and the concentrations of eight heavy metal elements (As, Cd, Cr, Cu, Mn, Ni, Pb and Zn) were determined by standard methods. The spatial distribution, pollution level and ecological risk status of heavy metals were analyzed based on GIS technology, the Geo-accumulation Index (Igeo), the Pollution Load Index (PLI) and the Potential Ecological Risk Index (RI). Results indicated that: (1) The average contents of Cd, Cr, Ni, Pb, and Zn of farmland soils exceeded the background values of irrigation soils in Xinjiang by 1.5, 1.40, 1.33, 2.63, and 4.92 times, respectively. Cd showed a no-pollution level, Zn showed a partially moderate pollution level, Pb showed a slight pollution level, and Cr, Cu, As, Mn, and Ni showed no-pollution level, compared to the classification standard. The PLI values of heavy metal elements of farmland soils varied from 0.83 to 1.89, with an average value of 1.29, at the moderate pollution level. (2) The Individual Potential Ecological Risk Index for heavy metals in the study area was ranked in the order of: As > Ni > Cu > Cd > Pb > Cr> Zn. The RI values of heavy metals of farmland soils varied from 3.45 to 11.34, with an average value of 6.13, at the low ecological risk level. (3) Cu and Mn of farmland soils were mainly originated from the soil parent material and topography of the study area. As, Cd, Ni and Pb were mainly originated from human activities, and Cr and Zn may originated from both natural and anthropogenic factors in the study area.

Evaluating Sediment Heavy Metal Pollution Level and Monitoring Network Representativeness at the Upstream Points of the Gangjeong-Goryeong Weir in the Nakdong River

Evaluating Sediment Heavy Metal Pollution Level and Monitoring Network Representativeness at the Upstream Points of the Gangjeong-Goryeong Weir in the Nakdong River

Distribution, source and pollution level of heavy metals in river sediments from South China

The sediment pollution caused by heavy metals has attracted a great deal of attention due to its persistence, bioaccumulation and toxicity. This research was the first to consider the whole of South China to obtain an overall profile of heavy metal spatial distribution, possible sources and pollution levels in river systems. For these data, 14 selected heavy metals were analysed in river sediments collected from sampling sites in Guangdong, Fujian, Guangxi and Hainan Provinces. The geoaccumulation index and enrichment factor revealed that river systems in South China were universally contaminated by Cd, As and Sn, which might be distributed by anthropogenic activities. Moreover, Guangdong Province, a relatively developed area in South China, was relatively polluted by certain heavy metals such as Ni, Cu, Zn and Mn. Multivariate statistical analyses such as Pearson's correlation matrix and a principal component analysis determined that several of the heavy metals might be derived from similar anthropogenic activities such as industrial effluents and domestic sewage discharge. In terms of heavy metal contamination in South China, necessary measures should be undertaken to protect rivers in South China.

Cultivation Ages Effect on Soil Physicochemical Properties and Heavy Metal Accumulation in Greenhouse Soils

The intensive management practices in greenhouse production may alter the soil physicochemical properties and contribute to the accumulation of heavy metals (HMs). To determine the HM concentrations in vegetable soil in relation to soil physicochemical properties and cultivation age, we conducted a soil survey for typical greenhouse soils in Shouguang, China. The results indicated that Cd is a major HM pollutant in the tested soils, as the only HM element exceeding the allowed limit for vegetable soil. The surveyed data was analyzed with regression analysis, correlation analysis and canonical correspondence analysis (CCA). A positive correlation is observed between HM pollution level and cultivation age. CCA results suggest that the HM pollution level and distribution in soil are significantly affected by soil physicochemical properties, which was a function of years of cultivation as revealed by regression analysis. In summary, cultivation age is an important factor to affect soil physicochemical properties (organic matter and inorganic nutrients) as well as HM contamination.

English

Surface water pollution poses a major risk to all biotic entities dependent on the water body. This study assessed the surface water quality of commodore channel, Lagos lagoon with respect to its heavy metals pollution level using indexing approach to determine the sources of heavy metal and its associated pollution risk. Samples were collected at a depth of 10-15 cm within a distance of 4 km from the shore line. Metal concentrations were evaluated using Atomic Absorption Spectrometry. The Concentrations of Pb (0.203-2.601 mg/L), Fe (0.253-1.049 mg/L), Cd (0.017-0.133 mg/L), and Co (0.000-0.226 mg/L) exceeded the recommended limits set by the World Health Organization, while Zn concentration (0.007-0.319 mg/L), was within acceptable limits for all locations investigated. Heavy metal pollution index (HPI) of the study area was found to be 3532.1, exceeding the critical pollution index value of 100. Similarly, the Metal Index (MI) of 150.5 of the study area was above threshold limit value of 1, suggesting that the area is seriously polluted with heavy metals. Sample t-test, confirms that there is a significant statistical different (with p value at p<0.05) between samples collected from the industrial areas and non-industrial area. The study revealed the sources of the heavy metals are primarily from anthropogenic source attributed to the untreated industrial discharge, and municipal solid waste disposed in the area. Prompt enforcement of environmental protection laws is needed to prevent continuous pollution of the area. Key words: Water quality, heavy metals, atomic absorption spectrometry, surface water, heavy metal pollution index, metal index.

Pollution characteristics and health risk assessment of heavy metals in the vegetable bases of northwest China

The objective of this study was to investigate heavy metal contamination in four major vegetable bases and determine the health risks of residents in the vicinity of the highly urbanized city Urumqi in Xinjiang, China. In this paper, we determined the contents of six heavy metals (i.e., As, Zn, Cd, Cr, Hg, and Pb) in surface soil and groundwater to evaluate the levels of heavy metal pollution and human health risks using the pollution index (PI), the Nemerow integrated pollution index (NIPI), the ecological risk factor (Eir), risk index (RI) and the health risk assessment model. The results showed that (1) The PI, NIPI, the ecological risk factor and risk index indicated that Cd and Hg were the primary pollutants in Sishihu village. These indices suggested moderate to slightly heavy potential ecological risks. In Anningqu town, Hg and Cd led to high levels of pollution and posed slightly heavy potential ecological risks. In Qinggedahu village, it was concluded that the metals Zn, Cr, Cd, Hg, and Pb caused moderate to heavy pollution. In Liushihu village, the pollution trends in the area were low. The results of the pollution level of the irrigation well water (i.e., groundwater) indicated that the well water was considerably safer than the soil, but Cr posed a slight pollution risk. (2) The non-carcinogenic risks for adults based on the HI values of these four vegetable bases were <1. However, when considering the non-carcinogenic risks for children, the HI values were larger than 1 in all areas, indicating the local children have a higher potential non-carcinogenic risk. In addition, CR (Carcinogenic risk) from dermal contact with the vegetables bases did not pose a high risk for residents. However, for adults, the carcinogenic risk posed by Arsenic (As) through trough inhalation was the primary pathway of exposure in three of the vegetable bases, generally in the order of Qinggedahu village > Sishihu village > Anningqu town. For children, the carcinogenic risks posed by As through trough inhalation and ingestion were the main exposure pathways. From the TCR results, it can be seen that in Sishihu village, Anningqu town, and Qinggedahu village, the TCR values for adults and children were >1 × 10−4 (unitless), and this degree of carcinogenic risk is unacceptable. (3) The identification of risk sources determined the main pollution sources affecting the vegetable bases were human activities and natural sources. Anthropogenic activities were most often related to traffic pollution sources and agricultural pollution sources, such as the irrational use of pesticides and fertilizers and stock farming. The results are important for designing remediation scenarios to control the spread of contamination as well as for serving as a reference point for soil environmental protection efforts in this region.

Analysis of Heavy Metal Pollution in Soil of Hechao Economic Development Zone

In order to understand the pollution level of soil heavy metals in Hechao Economic Zone of Anhui Province, 63 sampling sites were set up for soil sampling according to the actual conditions , and the concentrations of Cu, Hg, Ni, Pb, Cd, Cr, As and Zn were measured. The single pollution index method and Nemrow comprehensive pollution index method were used to evaluate the soil heavy metals in the study area. The results show that the detection points of Cu, Hg, Ni, Pb, Cd, Cr, As and Zn with 42.9%, 88.9%, 34.9%, 46%, 63.5%, 0, 18.8% and 100% respectively are above the standard Class One values. The results provide the necessary data support for the treatment of soil heavy metal pollution in Hechao economic development zone and also have important guiding significance for protecting the zone environment and carrying out the sustainable development of circular economy.

Investigation of heavy metal uptake by three types of ornamental plants as affected by application of organic and chemical fertilizers in contaminated soils

Accumulation of heavy metals in soil media is considered as a serious environmental problem, which is hazardous to human and animal health. There have been several methods for the removal of these toxic metals. One of the commonly used methods is the use of plants, especially ornamental plants to remove heavy metals from soils. In this regard, the study has been conducted on the soils contaminated with Mn, Pb, Ni, and Cd using factorial experiment in a completely randomized design with two factors including three types of soil (soil A for the highest level of contamination, B for the lowest level of pollution, and C for the non-contaminated soil) with different contamination levels as well as three types of ornamental plants, gladiolus, daffodils, and narcissus with four replications. In another part of the study, soil A and gladiolus were used in a completely randomized design with three replications, and also three types of fertilizers, such as municipal solid waste compost, triple superphosphate and diammonium phosphate, were added to this soil. In addition, the availability of heavy metal was studied in gladiolus as influenced by the application of organic and chemical fertilizers. The results showed that heavy metal pollution caused reduction in the dry weight of gladiolus and tulips compared to the control sample, while there was no significant effect of pollution on the dry weight of narcissus. The uptake of Mn, Pb, Ni, and Cd by all three plants has been increased with enhancing the pollution levels of heavy metals. The highest concentration of Pb in the shoots of plants was observed in soil A with an average amount of 61.16 (mg kg−1), which revealed a substantial difference relative to the treatment of soil B and C. The most and least amount of Ni in the plants shoots were related to soil A and soil C with an average of 2.35 and 0.89 mg kg−1, respectively. The uptake of Pb by shoots of all three plants was nearly similar to each other, while more Pb was absorbed by the bulbs of gladiolus compared to the bulbs of other plants. Increment in the pollution levels led to the decrement in enrichment factor (EF); however, there was no effect of pollution levels on EF of Mn and Pb. Moreover, there was no effect of increasing pollution levels on translocation factor of these elements. In gladiolus, after application of organic and chemical fertilizers, it was observed that the concentration of heavy metals was far more in the bulbs compared to the shoots. In conclusion, the cultivation of these ornamental plants is highly recommended due to not only their decorative aspect but also their ability for bioremediation as well as being economical.

Distribution of Heavy Metals and Minerals in the Various Size Fractions of Soil from Copșa Mică, România

The Copsa Mică area is one of the most polluted anthropic sites in Romania. Because higher heavy metal concentrations occur in finer fractions, this research focuses on the size fraction < 500 μm. Two kilograms soil sample was sieved on the 500-μm sieve and was air classified into size fractions down to the low micrometer range. The size fraction’s composition was investigated by ICP-OES IC, XRD, and FTIR spectrometry. Approximately 80 and 62% of the material was smaller than 2 mm and < 500 μm, respectively. The predominant size fraction had a mass median diameter (MMD) of approximately 75 μm. The smallest size fraction with a MMD of 2.2 μm had a share of 3.6% and contained the highest amount of heavy metals. The concentrations of Pb, Zn, Cd, Cu, Sb, and As exceeded the legally regulated values for soils according to Romanian legislation. The respective concentrations were 26,900, 27,600, 415, 2130, 466, and 915 mg·kg−1. In the coarser size fractions 5, 4, and 3, the predominant minerals were quartz and alkaline feldspar, while in the finer size fractions 1 and 2, the clay minerals and total carbon (TC) were predominant. Illites and montmorillonites in the fine fraction composition retain heavy metals due to the high levels of cation exchange capacity. Black carbon accumulated in soil acts as a heavy metal adsorbent due to its porosity and high specific surface area. The good correlation between heavy metals and TC in the top soil can be an indicator of the level of heavy metal pollution.

Effects of planting patterns on the concentration and bioavailability of heavy metals in soils during wetland restoration

To understand the effects of planting patterns on heavy metals in soils, the total concentration, bioavailability, contamination level, and ecological risk of heavy metals in soils from Jinjiang Estuary wetland were investigated. The results showed that after a wetland restoration, the concentrations of Cu were as follows: before wetland restoration > after wetland restoration > control group. The concentrations of Cr and Pb before and after the wetland restoration were all higher than those of the control group, whereas only some of the values of Zn were higher than those of the control group. Likewise, the bioavailability of Cu was roughly the same as that of the control group, those of Cr and Zn were higher than those of the control group, and that of Pb was less than that of the control group. Generally, after the wetland restoration, the bioavailabilities of Cu, Cr, and Pb decreased, but that of Zn increased. Moreover, the pollution level and ecological risk of Cu decreased, while those of Cr, Zn, and Pb increased. In addition, the comprehensive potential ecological risk of the Jinjiang Estuary wetland was moderate for Cu, Cr, Zn, and Pb before and after the wetland restoration. These results suggest that during a wetland restoration, the mixed vegetation types and planting density could influence the total concentration and bioavailability of heavy metals, affecting the pollution level and ecological risk of heavy metals to some extent. This study would be helpful in providing subsequent scientific research to restore wetlands.

Impact of Heavy Metal Pollution on Ammonia Oxidizers in Soils in the Vicinity of a Tailings Dam, Baotou, China.

Soil heavy metal pollution has received increasing attention due to their toxicity to soil microorganisms. We have analyzed the effects of heavy metal pollution on ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in soils in the vicinity of a tailings dam of Baotou region, China. Results showed that AOB were dominated with Nitrosomonas-like clusters, while AOA was dominated by group1.1b (Nitrososphaera cluster). Single Cd and Cr contents, as well as compound heavy metal pollution levels, had a significant negative impact on soil potential nitrification rate and both diversities of AOA and AOB. No clear relationship was found between any single heavy metal and abundance of AOA or AOB. But compound pollution could significantly decrease AOA abundance. The results indicated that heavy metal pollution had an obviously deleterious effect on the abundance, diversity, activity and composition of ammonia oxidizers in natural soils.