Polycyclic Aromatic Hydrocarbons In Urban Soils Research Articles

Black carbon, soil organic matter molecular signatures under different land uses in Shenyang, China and relationship with PAHs

The content, composition and molecular signatures of soil organic matter (SOM) have important influences on the cycle of soil organic carbon (SOC) and the partitioning of polycyclic aromatic hydrocarbons (PAHs) in soil. Seventy-nine soil samples from farmland, forest and urban areas were collected in Shenyang, China to investigate black carbon (BC) content, SOM molecular signatures varied with land use patterns, as well as the relationship with PAHs. The content of BC in urban soils was significantly higher than that of farmland and forest. BC was a key contributor of urban SOM which accounted for 0.35 ± 0.31 of SOC in urban soil. Based on BC/SOC ratio, the main sources of BC were identified as fossil fuel combustion for urban soils, while for farmland and forest soils, it is the mixed results of fossil fuel combustion and biomass burning. All categories of PAHs in urban soils showed the highest level compared to farmland and forest soils. Pearson's correlation analysis results showed there were significant positive correlations between BC and PAHs categories in urban soils, indicating the important role of BC in the accumulation of PAHs in soil. SOM from each of the two different land use patterns can be distinguished by molecular signatures. Urban SOM had abundant molecular markers derived from condensed organic carbon inputs, which was consistent with the BC/SOC value. Farmland SOM had abundant carbon from vegetation and microorganisms, and forest SOM was rich in organic carbon from fresh plant materials. The markers enriched in urban SOM showed significant correlations with most PAHs categories, highlighting the affinity of urban SOM for PAHs at the molecular level. This study contributed to understanding the impact of land management methods on SOM molecular composition signatures and its influence on PAHs occurrence in soil, providing a theoretical basis for regional soil pollution management.

An improved hybrid model on source-risk of polycyclic aromatic hydrocarbon in soils of the Yangtze River Delta urban agglomeration.

The source, exposure and risks of polycyclic aromatic hydrocarbons (PAHs) in soil environments are of great importance to evaluate soil quality. However, understanding the risks of specific sources of PAHs in soils remains poorly understood. In this study, we determined the source, exposure and risks of PAHs in the Yangtze River Delta urban agglomeration. The source analysis receptor model combined with land use types significantly increased the identification of pollution sources and improved the prediction accuracy of PAH concentrations. There is a strong correlation between the measured and predicted values of high ring PAH. The correlations of BbF, InP and Pyr are 0.947, 0.896 and 0.906 respectively, which is significantly higher than the unmodified model. By combining the ecological risk assessment and health risk assessment models of PAHs, we established an improved mixed source-risk model. The PAHs in urban soils had the highest ecological risk and health risk, with risk probabilities of 56.3 % and 28.2 %, respectively. The average contamination severity index values of PAHs caused by oil combustion sources, coal combustion sources, coking furnace sources, and fuel (biomass, petroleum, and diesel) combustion sources were 0.13, 0.10, 0.16 and 0.17, respectively. The average noncarcinogenic risks of PAHs from oil combustion sources, coal combustion sources, coking furnace sources and biomass, petroleum volatilization and diesel combustion sources to children were 0.12, 0.11, 0.08 and 0.13, respectively. Approximately half of the PAH pollution risk in forestland and grassland soil were associated with the combustion of petroleum fossil fuels. This study quantitatively analyzed the contribution of different PAHs pollution sources in different land types of soils, further calculated the risks of each pollution source to the ecological environment and human health, and proposed corresponding treatment measures, which provided scientific and systematic methods and technologies for soil pollution management in other regions of the world.

Microbiological status of natural and anthropogenic soils of the Taganrog Bay coast at different levels of combined pollution with heavy metals and PAHs.

The effect of heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) pollution on the microbiological status of soils on the coast of the Taganrog Bay and adjacent areas was studied. The content of total and exchangeable forms of HMs, the content of 16 priority PAHs and the abundance of several groups of culturable microorganisms was determined, namely copiotrophic, prototrophic, aerobic spore-forming bacteria, actinomycetes, molds and yeasts. The content of total and exchangeable forms of HMs in urban coastal soils in industrial zone significantly exceeded that in non-urban soils. The maximum concentrations of total forms of Mn, Cr, Ni, Cu, Zn, Pb and Cd are 1821, 871, 143, 89, 1390, 317 and 10mg/kg, respectively. The median value of the total content of 16 PAHs in urban soils is 3 times higher than in the soils of natural areas and reached 4309ng/g. The lowest numbers of copiotrophic bacteria, prototrophic bacteria and aerobic spore-forming bacteria were found in the soils of industrial zone: 6.8, 13.8 and 0.63million CFUg-1 dry soil, respectively. The largest numbers of copiotrophic bacteria, prototrophic bacteria and aerobic spore-forming bacteria were recorded in the soils of natural areas-72.5, 136 and 5.73million CFUg-1 dry soil, respectively. It was found that the abundance of copiotrophs, prototrophs, and aerobic spore-forming bacteria is more affected by the urbanization of coastal soils including the pollution of HMs and PAHs. Other groups of microorganisms (actinomycetes, molds and yeasts) turned out to be more resistant to anthropogenic factors.

Characterization, source apportionment, and risk assessment of polycyclic aromatic hydrocarbons (PAHs) in urban soils from 23 cities in China.

Concentrations, composition profiles, sources, and health risks of 16 USEPA priority polycyclic aromatic hydrocarbons (PAHs) in urban soils from 23 cities across China based on metadata collected from previous studies between 2005 and 2021 were investigated. ΣPAH concentrations in urban soils from 23 cities across China ranged from 0.1231 to 17.2000mg/kg (mean = 2.7171 ± 3.8276mg/kg). Overall PAH contamination in urban soils across China was moderate compared to that in global cities. Based on energy consumption and climate conditions, the spatial distributions of mean ΣPAH concentrations in Northeast China were highest, followed by those in North China, West China, East China, and South China. Individual PAH composition profiles decreased in the order: 4-ring PAHs (41.36%) > 5-ring PAHs (21.77%) > 3-ring PAHs (18.53%) > 6-ring PAHs (14.00%) > 2-ring PAHs (2.27%). Diagnostic ratios and positive matrix factorization (PMF) revealed that PAHs in urban soils were mainly derived from fossil fuel combustion (from coal, natural gas, and biomass), especially in North, Northeast, and East China, with smaller contributions from petrogenic sources. Health risk assessment results suggest that although there are potential cancer risks from PAHs, risks were acceptable. Toxic equivalent concentration (TEQ) and the corresponding oral cancer slope factor (CFS0) contributed most to the uncertainty of total risks. This study will help develop strategies to reduce PAH risk management in urban soils in China.

Formation mechanism of soil PAH distribution: High and low urbanization

Urbanization is an important driving force for the distribution of polycyclic aromatic hydrocarbons (PAHs) in urban soils. Research on factors affecting PAH distribution in urban soils has focused on analyses of statistical relationships, and quantitative models are not available in the literature. Accordingly, we chose the urban area of Nanjing (high urbanization), and Dingshu (low urbanization), and then comprehensively utilized soil sample test analyses, multivariate statistics, and other technical means to (1) study the concentration and sources of PAHs in urban soils, and (2) identify the main controlling factors that affect urban soil PAH distribution. We found that the population density and black carbon (BC) components were the critical factors of soil PAH distribution in Nanjing, yet BC components and leaf area index in Dingshu. We then constructed a quantitative relationship model of urban soil PAH distribution in different levels of urbanization. Using this model, we conducted a preliminary analysis of the formation mechanism of urban soil PAHs under different urbanization levels. This research provides a basis for finely controlling regional urban soil PAH pollution.

Novel and specific source identification of PAH in urban soils: Alk-PAH-BPCA index and “V”-shape distribution pattern

Soils in urban and industrial areas, especially in larger metropolitan areas such as the Ruhr area, Germany, are commonly characterized by severe anthropogenic overprinting due to urbanization processes including land development measures. Such urban soils often contain various anthropogenic substrate admixtures, like ash, coal, tailings, building rubble, industrial waste materials, as well as urban dust, soot, fly ash, and others. These admixtures often carry higher contents of pollutants such as polycyclic aromatic hydrocarbons (PAH). Whereas elevated PAH concentrations are commonly attributed to non-point pyrogenic carbon sources like soot and particulate matter, petrogenic PAH sources are still largely neglected in this context.In this study, an extended sample set of 62 samples of PAH source materials and urban soils containing anthropogenic substrate components was investigated by combining extended PAH analysis of 59 PAH, alkylated PAH distributions and benzene polycarboxylic acid (BPCA) analysis with regard to petrogenic and pyrogenic PAH source identification. For more reliability of source apportionment by a more integrative signal, the alkylated PAH distributions of different PAH groups were combined according to their degrees of alkylation. Based on this combination, a new PAH alkylation index (ΣC0/(ΣC0+ΣC2)) was derived, which considers, in contrast to commonly used single PAH ratios, a series of non-alkylated and alkylated PAH.By comparison of this PAH alkylation index with the degree of aromatic condensation a new robust and economic method for identifying petrogenic, pyrogenic and mixed PAH sources within soil samples and sediments was developed. It is shown that coal and coal ash particles are a not negligible PAH source in urban soils of mining-dominated regions and can make up a large proportion of the anthropogenic substrate components encountered.Further analyses of samples with defined levels of petrogenic and pyrogenic PAH are necessary to finally evaluate the usefulness of this proposed new PAH-BPCA approach.

Distribution, source apportionment, and health risk assessment of polycyclic aromatic hydrocarbons in urban soils from Shenyang, China.

A total of 74 urban topsoil samples were collected from the central area of Shenyang, China. The concentration, distribution, source, and health risk of 16 polycyclic aromatic hydrocarbons (PAHs) were analyzed. The 16 USEPA priority PAHs were detected in all soil samples. The total concentrations of PAHs ranged from 283 to 21,821ng/g dry weight (dw), with a mean value of 2370ng/g and median value of 1427ng/g. The benzo[a]pyrene toxicity equivalent (BaPeq) concentrations ranged from 6.03 to 2403ng/g dw, with a mean value of 308ng/g and median value of 185ng/g. High molecular weight PAHs were the predominant components. The spatial distribution revealed that soil PAH concentrations within the Two Ring Road were high, but low in the south of Hun River. Compared with other urban soils, the pollution of PAHs in urban soils of Shenyang was at a moderate level, but increased rapidly compared with previous years, especially fluoranthene. Diagnostic ratios of PAHs and positive matrix factorization model all suggested that PAHs in urban soils of Shenyang were dominantly from pyrogenic origins. The health risk assessment indicated that children had the highest total carcinogenic risk, followed by adolescents and adults. The differences between gender groups for the same age group were insignificant. Ingestion was the dominant exposure pathway, followed by dermal contact and inhalation. The total lifetime carcinogenic risks at all sampling sites were lower than the highest acceptable risk (10-4), and those of Eastern, Central, and Western Shenyang were higher than those of Northern and Southern Shenyang.

Levels, sources, and toxicity assessment of polycyclic aromatic hydrocarbons in urban topsoils of an intensively developing Western Siberian city.

This study investigates the levels, sources, spatial distribution, and toxicity of polycyclic aromatic hydrocarbons (PAHs) in urban soils of Tyumen, Russia. Observations of PAHs in cities of Western Siberia accomplished by a representative set of samples are very rare, even though it is one of the most urbanized parts of Russia. Therefore, it is important to estimate the status of PAHs in soils of urban environments representing vast Siberian regions. Tyumen, as one of the most intensively developing cities of Western Siberia, is a good object for such studies. Topsoil samples (0-10cm) were collected from 241 sampling sites on a regular grid within Tyumen city limits. It was found that total concentration of 12 priority PAHs ranged from 33.4 to 2147.9μgkg-1, with a median value of 280.3μgkg-1. High-molecular-weight (HMW) PAHs were dominant, accounting for the majority (62%) of the total PAHs. Among the PAHs in soils, 4-ring compounds were predominant in all studied samples, followed by 5- and 6-ring PAHs. Phenanthrene, pyrene, fluoranthene, and benzo(ghi)perylene had values of 28%, 19%, 15%, and 10% of total PAHs, respectively. Results showed that large high-contrast anomalies of HMW PAHs were related to low-residential and transport areas. The diagnostic ratios, as well as hierarchical cluster analysis (HCA) and principal component analysis (PCA), confirmed that sources associated with the transport were the most significant, while biomass combustion played an important role as a source of PAHs in agricultural, low-residential, and recreational areas. Levels of individual PAHs, as well as total PAHs in urban soils of Tyumen, were comparable with those in non-industrial cities with similar populations but were significantly lower than those in large industrial centers. Assessment of soil toxicity using toxic equivalent quantity (TEQBaP) showed that the TEQBaP values varied from 2.0 to 388.2μgkg-1, with a mean value of 34.9μgkg-1 and median of 19.8μgkg-1, and were lower than those in heavy industrialized cities, but higher than those in soils of cities specializing in consumer and service industries.

Emerging and legacy PAHs in urban soils of four small cities: Concentrations, distribution, and sources

Polycyclic aromatic hydrocarbons (PAHs) are widespread organic contaminants in the environment, much being accumulated in soils. Although their concentrations in large cities have been studied, their levels in small cities were less studied. This study determined the concentrations, distributions, and sources of 16 USEPA priority PAHs (legacy PAHs) and 6 emerging PAHs in urban soils of four small cities. A total of 100 soil samples were collected in Florida, USA. The average ∑16-PAHs in urban soils of Clay county, Ocala, Pensacola, and West Palm Beach were 1821, 2748, 3115 and 4055 μg kg−1, respectively. Based on benzo[a]pyrene-equivalent (BaP-EQ), the 7 USEPA carcinogenic PAHs (7cPAHs) and 3 emerging carcinogenic PAHs (3cPAHs) in urban soils in Clay County averaged 223 and 3703, Ocala 319 and 4521, Pensacola 302 and 5423, and West Palm Beach 449 and 5916 μg kg−1, respectively. Although ∑7cPAHs in 87–89% of samples were lower than the Florida Soil Cleanup Target Levels (FSCTLs) for industrial sites at 700 μg kg−1, ∑3cPAHs were 13–18 times greater than ∑7cPAHs. Based on the PMF model and molecular diagnostic ratios, soil PAHs were dominated by similar sources in small cities, mainly from pyrogenic sources including biomass, coal and coke combustion and vehicle emissions. It is important to evaluate both legacy and emerging PAHs concentrations in urban soils when considering soil remediation and human health risk assessment.

Emerging PAHs in urban soils: Concentrations, bioaccessibility, and spatial distribution

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous organic contaminants, with soil being the most important sink. This study determined the concentrations, bioaccessibility and spatial distributions of 6 emerging PAHs in Orlando and Tampa urban soils. They included 3 carcinogenic (anthanthrene, 7H-benzo[c]fluorene, and dibenzo[a,l]pyrene: 3cPAHs) and 3 non-carcinogenic (dibenzo[a,e]pyrene, dibenzo[a,i]pyrene and dibenzo[a,h]pyrene) PAHs. Based on benzo[a]pyrene-equivalent, the 7 USEPA priority cPAHs (7cPAHs) and 3cPAHs in Orlando soils averaged 452 and 7387 μg kg−1, and Tampa soils 802 and 4943 μg kg−1, respectively, with ∑3cPAHs being 6–16 times greater than ∑7cPAHs. Based on ArcGIS maps, the concentrations of ∑3cPAHs in commercial sites, business district and heavy-traffic areas were higher. The concentrations of ∑3cPAHs have not been reported, but they had significant impacts on risk assessment of urban soils due to their high relative potency factor. However, their bioaccessibility based on n-butanol extraction in soils of both cities were low, averaging 3.4–7.4%. Therefore, to accurately assess the risk of soils contaminated with PAHs, emerging cPAHs together with USEPA 7cPAHs and their bioaccessibility need to be considered.

Multivariate Analysis for Assessing Sources, and Potential Risks of Polycyclic Aromatic Hydrocarbons in Lisbon Urban Soils

Urban soils quality may be severely affected by polycyclic aromatic hydrocarbons (PAHs) contamination, as is the case of Lisbon (Portugal). However, to conduct a risk assessment analysis in an urban area can be a very difficult task due to the patchy nature and heterogeneity of these soils. Thus, the present study aims to provide an example on how to perform the first tier of a risk assessment plan in the case of urban soils using a simpler, cost effective, and reliable framework. Thus, a study was conducted in Lisbon to assess the levels of PAH, their potential risks to the environment and human health, and to identify their major sources. Source apportionment was performed by studying PAHs profiles, their relationship with potentially toxic elements, and general characteristics of soil using multivariate statistical methods. Results showed that geostatistical tools are useful for evaluating the spatial distribution and major inputs of PAHs in urban soils, as well as to identify areas of potential concern, showing their usefulness in risk assessment analysis and urban planning. Particularly, the prediction maps obtained allowed for a clear identification of areas with the highest levels of PAHs (close to the airport and in the city center). The high concentrations found in soils from the city center should be a result of long-term accumulation due to diffuse pollution mostly from traffic (through atmospheric emissions, tire debris and fuel exhaust, as well as pavement debris). Indeed, most of the sites sampled in the city center were historical gardens and parks. The calculation of potential risks based on different models showed that there is a high discrepancy among guidelines, and that risks will be extremely associated with the endpoint or parameters used in the different models. Nevertheless, this initial approach based on total levels was useful for identifying areas where a more detailed risk assessment is needed (close to the airport and in the city center). Therefore, the use of prediction maps can be very useful for urban planning, for example, by crossing information obtained with land uses, it is possible to define the most problematic areas (e.g., playgrounds and schools).

PAHs in urban soils of two Florida cities: Background concentrations, distribution, and sources

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous organic contaminants, which are found in soils throughout the U.S. The objective of this study was to determine the background concentrations, distributions, and sources of 16 USEPA priority PAHs in two urban soils. A total of 114 soil samples were collected from two large cities in Florida: Orlando and Tampa. The results showed that soils were dominated by high molecular weight PAHs in both cities. The average ∑16-PAHs in Orlando and Tampa soils were 3227 and 4562 μg kg−1, respectively. The averages of 7 carcinogenic PAHs based on the benzo[a]pyrene-equivalent (BaP-EQ) concentrations in the two cities were 452 and 802 μg kg−1. BaP-EQ concentrations in 60–62% of samples were higher than the Florida Soil Cleanup Target Level (FSCTL) for residential soils at 100 μg kg−1 and 20–25% of samples were higher than FSCTL for industrial soils at 700 μg kg−1. Based on molecular diagnostic ratios and PMF modeling, major sources of soil PAHs in both cities were similar, mainly from pyrogenic sources including vehicle emissions, and biomass and coal combustion. Based on ArcGIS mapping, PAH concentrations in soils near business districts and high traffic roads were higher. Thus, it is important to consider background PAH concentrations in urban soils when considering soil remediation.

Polycyclic Aromatic Hydrocarbons in Urban Soil in the Semi-arid City of Xi'an, Northwest China: Composition, Distribution, Sources, and Relationships with Soil Properties.

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the environment. This study collected a total of 62 urban soil samples from the typical semi-arid city of Xi'an in Northwest. They were analyzed for the composition, distribution, and sources of PAHs as well as the relationships with soil properties. The sum of 16 individual PAHs (∑16PAHs) ranged from 390.6 to 10,652.8μg/kg with a mean of 2052.6μg/kg. The average ∑16PAHs decreased in the order of the third ring road (2321.1μg/kg) > the first ring road (1893.7μg/kg) > the second ring road (1610.0μg/kg), and in the order of industrial areas (3125.6μg/kg) > traffic areas (2551.6μg/kg) > educational areas (2414.4μg/kg) > parks (1649.5μg/kg) > mixed commercial and traffic areas (1332.8μg/kg) > residential areas (1031.0μg/kg). The most abundant PAHs in the urban soil were 3- to 5-ring PAHs. Elevated levels of PAHs were found in industrial and traffic areas from the east and west suburbs and the northwest corner of Xi'an as well as the northeast corner in the urban district of Xi'an. PAHs in the urban soil were mainly related to the combustion of fossil fuel (i.e., coal, gasoline, diesel, and natural gas) and biomass (i.e., grass and wood) (variance contribution 57.2%) as well as the emissions of petroleum and its products (variance contribution 29.9%). Soil texture and magnetic susceptibility were the main factors affecting the concentration of PAHs in urban soil. Meanwhile, this study suggested that the single, rapid, and nondeductive magnetic measurements can be an indicator of soil pollution by PAHs.

Distribution, sources, and air–soil exchange of OCPs, PCBs and PAHs in urban soils of Nepal

Due to the high temperature and extensive use of organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs), tropical cities could act as secondary sources of these pollutants and therefore received global concern. As compared with other tropical cities, studies on the air–soil exchange of OCPs, PCBs and PAHs in tropical Nepali cities remained limited. In the present study, 39 soil samples from Kathmandu (capital of Nepal) and 21 soil samples from Pokhara (second largest city in Nepal) were collected The soil concentrations of the sum of endosulfans (α- and β-endosulfans) ranged from 0.01 to 16.4 ng/g dw. Meanwhile, ∑dichlorodiphenyltrichloroethane (DDTs) ranged from 0.01 to 6.5 ng/g dw; ∑6PCBs from 0.01 to 9.7 ng/g dw; and ∑15PAHs from 17.1 to 6219 ng/g dw. High concentrations of OCPs were found in the soil of commercial land, while, high soil PAH concentrations were found on tourist/religious and commercial land. Combined the published air concentrations, and the soil data of this study, the directions and fluxes of air–soil exchange were estimated using a fugacity model. It is clear that Nepal is a country contributing prominently to secondary emissions of endosulfans, hexachlorobenzene (HCB), and low molecular weight (LMW) PCBs and PAHs. The flux for all the pollutants in Kathmandu, with ∑endosulfans up to 3553; HCB up to 5263; and ∑LMW-PAHs up to 24378 ng m−2 h−1, were higher than those in Pokhara. These high flux values indicated the high strength of Nepali soils to act as a source.

Sources and Risk Assessment of Polycyclic Aromatic Hydrocarbons from the Urbanization Process of Topsoil

To study the effects of urbanization on concentration, sources, and health risks of polycyclic aromatic hydrocarbons (PAHs), 95 topsoil samples were collected from Liaoning Province. For this assessment, 21 PAHs were analyzed via gas chromatography-mass spectrometry and discussed. The results show the total concentrations of the 21 PAHs in background, Shen-Fu, Shen-Yang, and Fu-Shun were 1496.76 μg·kg-1, 3000.50 μg·kg-1, 8705.11 μg·kg-1, and 8178.90 μg·kg-1, respectively, which is positively correlated with the urbanization levels. Diagnostic ratios and PMF modal analysis indicate that the sources of the PAHs in soils were most likely coal combustion and traffic combustion (petroleum combustion). The main sources of PAHs in the four areas were petrochemical combustion (41.0%), coal combustion (64.4%), traffic combustion (67.5%), and traffic combustion (62.0%), that is, with the urbanization process, human activity (mainly traffic combustion) gradually become the major contributor of PAHs to the environment. Health risk assessment showed that the risk of cancer exposure through soil digestion and skin exposure was higher. There is a higher health risk from PAHs in urban soils, and the health risks associated with children and adolescents are greater than with other residents, requiring more attention.

Availability of polycyclic aromatic hydrocarbons to earthworms in urban soils and its implications for risk assessment

Polycyclic aromatic hydrocarbons (PAHs) are a global problem, and in urban soils they can be found at potentially hazard levels. Nevertheless, the real risks that these contaminants pose to the environment are not well known, since the bioavailability of PAHs in urban soils has been poorly studied. Therefore, the bioavailability of PAHs in some selected urban soils from Lisbon (Portugal) was evaluated. Moreover, the applicability of a first screening phase based on total contents of PAHs was assessed. Results show that bioavailability of PAHs is reduced (low levels in earthworms, low accumulation percentages, and low biota-to-soil accumulation factors values), especially in more contaminated soils. The aging of these compounds explains this low availability, and confirms the generally accepted assumption that accumulation of PAHs in urban areas is mostly related with a long-term deposition of contaminated particles. The comparison of measured PAHs concentrations in earthworm tissues with the ones predicted based on theoretical models, reinforce that risks based on total levels are overestimated, but it can be a good initial approach for urban soils. This study also highlights the need of more reliable ecotoxicological data.

Polycyclic Aromatic Hydrocarbons (PAHs) in Exposed-Lawn Soils from 28 Urban Parks in the Megacity Guangzhou: Occurrence, Sources, and Human Health Implications

Polycyclic aromatic hydrocarbons (PAHs) in urban soils may pose a serious threat to human health via oral ingestion, dermal absorption, and particulate inhalation, especially in public parks and playgrounds, with children and senior citizens showing the highest susceptibility. Several studies have been undertaken identifying PAHs in urban soils, but no studies to date have assessed PAHs in urban parks, in particular in exposed-lawn soils. In recent decades, unprecedented rates of urbanization and industrialization in China have resulted in significant levels of urban environmental pollution. However, concentrations, sources, and the health risk associated with PAH exposure via urban park lawn soils in China remain unknown. The concentrations, sources, and health risk of exposure to 16 PAHs in surface-exposed lawn soils were studied in 28 urban parks in Guangzhou. Concentrations of Σ16PAHs ranged from 76.44 to 890.85ng/g with a mean of 286.11ng/g. PAH composition was mostly characterized by 2- and 4-ring PAHs in most sampling parks; Nap, Flua, Pyr, Phe, and Chr were the dominant constituents. Principle component analysis coupled with multivariate linear regression indicated that vehicular and coal combustion emissions contributed to 50.53 and 49.46% of PAHs in Guangzhou's urban park soils, respectively. Total cancer risk (TCR) analysis found that 22 parks (accounting for 78.57% total parks) designed for children's use and general-use park areas presented a potentially high risk (>1×10-4) for all users.

Distribution, compositional pattern and sources of polycyclic aromatic hydrocarbons in urban soils of an industrial city, Lanzhou, China

The level, distribution, compositional pattern and possible sources of polycyclic aromatic hydrocarbons (PAHs) in Lanzhou urban soil of Northwest China were investigated in this study. The total level of 22 PAHs ranged from 115 to 12,100µgkg−1 and that of 16 priority PAHs from 82.4 to 10,900µgkg−1. Seven carcinogenic PAHs generally accounted for 6.18–57.4% of total 22 PAHs. Compared with data from those reported about urban areas, PAH contamination in Lanzhou urban soils was moderate. Among different functional areas, higher level of PAHs was found along roadsides and in the industrial district (p<0.01), while lower levels were detected in the commercial, park and residential districts. The composition of PAHs was characterized by high molecular weight PAHs (≥4 rings), among which fluoranthene, benz[a]anthracene and phenanthrene were the most dominant components. Correlation analysis suggested that low molecular weight PAHs and high molecular weight PAHs originated from different sources and further corroborated that TOC was an important factor in the accumulation of PAHs in soil. Isomer ratios and principal component analysis indicated that PAHs in urban soil derived primarily from emissions resulting from the combustion of biomass, coal and petroleum products. Toxic equivalent concentrations (BaPeq) of soil PAHs ranged from 6.12 to 1302µgBaPeqkg−1, with a mean of 138µgBaPeqkg−1. The results suggested that human exposure to those soils which polluted by high concentrations of PAHs through direct ingestion or inhalation of suspended soil particles probably poses a significant risk to human health from the carcinogenic effects of PAHs.

Black carbon in soils from different land use areas of Shanghai, China: Level, sources and relationship with polycyclic aromatic hydrocarbons

Black carbon (BC) in soils plays a key role of carrying hydrophobic pollutants like polycyclic aromatic hydrocarbons (PAHs). However, little is known about the spatial distribution, sources of BC and its relationship with PAHs in urban soils. We studied BC, total organic carbon (TOC) and PAHs concurrently in 77 soils collected from downtown area, suburban and rural area and industrial area of Shanghai, China. BC was determined by both chemical oxidation (dichromate oxidation, BCCr) and chemo-thermal oxidation (CTO-375, BCCTO). BC sources were identified qualitatively by BC/TOC concentration ratios and BC-cogenerated high molecular weight (HMW) PAH isomer ratios and quantitatively by principal component analysis followed by multiple linear regression (PCA-MLR). Results showed that BCCr concentration (4.65g/kg on average) was significantly higher than BCCTO (1.91g/kg on average) in Shanghai soils. BCCr concentrations in industrial area were significantly higher than those in other two. Stronger correlation was found between PAHs and TOC, BCCr than that between PAHs and BCCTO, which indicates the possibility of PAHs being carried by charcoal and other organic matters thus negating its exclusive dependence on soot. Charcoal was therefore suggested to be taken into account in studies of BC and its sorption of PAHs. BC/TOC ratios showed a mixed source of biomass burning and fossil fuel combustion. PCA scores of BC-cogenerated HMW PAHs isomer ratios in potential sources and soil samples clearly demonstrated that sources of BC in urban soils may fall into two categories: coal and biomass combustion, and traffic (oil combustion and tire wear). PCA-MLR of HMW PAHs concentrations in soil samples indicated that coal and oil combustion had the largest contribution to BC in urban soils while tire wear and biomass combustion were important in downtown and rural area, respectively, which indicated they were main sources of HMW PAHs and presumably of BC.

Levels and sources of polycyclic aromatic hydrocarbons (PAHs) in selected irrigated urban agricultural soils in Accra, Ghana

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous organic pollutants in urban environments including urban soils. Elevated concentrations of PAHs in urban soils are caused by incomplete combustion of petroleum and coal. This study assesses 16 individual PAH compounds in a total of 112 surficial soil samples. The objective was to assess and compare the levels of contamination as well as examine the main sources of PAHs in four urban agricultural soils using molecular ratios of some specific hydrocarbons. The study showed that PAH levels in soil ranged from 1.23 ng/kg in soil collected from Dzorwulu to 2.95 ng/kg in soil collected from Ghana Broadcasting Cooperation (GBC) vegetable irrigation site. Of the total PAHs, the more water soluble PAHs (2–4 rings), which tend to be concentrated in the vapour phase were found to dominate the soils. The percentage dominance were Dzorwulu (52.8 %), Marine Drive (62.5 %), CSIR (53.2 %) and GBC (49.2 %). However, there were significant levels of the more carcinogenic PAHs (5–6 rings) present with percentages as 47.1, 37.5 46.8 and 50.8 % for Dzorwulu, Marine Drive, CSIR and GBC vegetable irrigation sites, respectively, and therefore, may impact negatively on public health. Based on the classification by the Institute of Soil Science and Plant Cultivation in Pulawy, Poland, urban soils in Accra could be classified as contaminated to different levels. Molecular ratios of Flu/pyr and PA/Ant were calculated to determine the main sources of PAHs. Results showed that PAHs could originate mainly from incomplete combustion of petroleum products, especially from atmospheric fallout from automobile exhausts. The study further showed that B(a)P concentration of 0.05 ng/kg in soil from GBC urban vegetable irrigation site requires immediate clean-up exercise and monitoring to mitigate human health impact.