PAH depositional history and sources in recent sediment core from Ukwa Ibom Lake, S. E. Nigeria

Exploring organic and inorganic contaminant histories in sediment cores across the anthropocene: Accounting for site/area dependent factors

Sedimentary records help chronologically identify anthropogenic contamination in environmental systems. This study analysed dated sediment cores from L'Albufera Lake (Valencia, Spain), to assess the occurrence of heavy metals (HMs), polycyclic aromatic hydrocarbons (PAHs), perfluoroalkyl substances (PFASs), organophosphorus flame retardants (OPFRs), pesticides and pharmaceuticals and personal care products (PPCPs). The results evidence the continuing vertical presence of all types of contaminants in this location. The sediment age was difficult to establish. However, the presence of shells together with an historical estimation and the knowledge of sedimentary rates could help. HMs contents are higher in the upper layer reflecting the most recent increase of the industrial and agricultural practices in the area since the middle 20th century. Higher availability index of these HMs in the upper sediment layers is associated with point and diffuse contamination sources in the area. PAHs and OPFRs were homogeneous distributed through the sediments with few exceptions such as phenanthrene in the North and fluoranthene in the South. Perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS) were detected throughout the sediment core while short-chain PFASs (except perfluoropentanoic acid (PFPeA)) were detected only in the top layer. Pesticides and PPCPs showed appreciable down-core mobility. The vertical concentration profiles of organic contaminants did not exhibit a clear trend with depth, then, it is difficult to develop a direct relationship between sediment age and contaminant concentrations, and to elucidate the historical trend of contamination based on dated sediment core. Consequently, linking contaminant occurrence in sediments directly to their historical use is somewhat speculative at least in the conditions of L'Albufera Lake.

Occurrence, sources and health risk of polycyclic aromatic hydrocarbons in soils around oil wells in the border regions between oil fields and suburbs

The Yellow River Delta (YRD) is a typical region where oil fields generally overlap cities and towns, leading to complex soil contamination from both the oil fields and human activities. To clarify the distribution, speciation, potential sources and health risk of polycyclic aromatic hydrocarbons (PAHs) in soils of border regions between oil fields and suburbs of the YRD, 138 soil samples (0-20 cm) were collected among 12 sampling sites located around oil wells with different extraction histories. The 16 priority control PAHs (16PAHs), as selected by the United States Environmental Protection Agency (USEPA), were extracted via an accelerated solvent extraction and detected by GC-MS. The results showed that soils of the study area were generally polluted by the 16PAHs. Among these pollutions, chrysene and phenanthrene were the dominant components, and 4-ring PAHs were the most abundant. A typical temporal distribution pattern of the 16PAHs was revealed in soils from different sampling sites around oil wells with different exploitation histories. The concentrations of total 16PAHs and high-ring PAHs (HPAHs) both increased with the extraction time of the nearby oil wells. Individual PAH ratios and PCA method revealed that the 16PAHs in soil with newly developed oil wells were mainly from petroleum pollutants, whereas PAHs in soils around oil wells with a long exploitation history were probably from petroleum contamination; combustion of petroleum, fuel, and biomass; and degradation and migration of PAHs from petroleum. Monte Carlo simulation was used to evaluate the health risks of the 7 carcinogenic PAHs and 9 non-carcinogenic PAHs in the study area. The results indicated that ingestion and dermal contact were the predominant pathways of exposure to PAH residues in soils. Both the carcinogenic and non-carcinogenic burden of the 16PAHs in soils of the oil field increased significantly with exploitation time of nearby oil wells.

Accumulation, allocation, and risk assessment of polycyclic aromatic hydrocarbons (PAHs) in soil-Brassica chinensis system

Farmland soil and leafy vegetables accumulate more polycyclic aromatic hydrocarbons (PAHs) in suburban sites. In this study, 13 sampling areas were selected from vegetable fields in the outskirts of Xi'an, the largest city in northwestern China. The similarity of PAH composition in soil and vegetation was investigated through principal components analysis and redundancy analysis (RDA), rather than discrimination of PAH congeners from various sources. The toxic equivalent quantity of PAHs in soil ranged from 7 to 202 μg/kg d.w., with an average of 41 μg/kg d.w., which exceeded the agricultural/horticultural soil acceptance criteria for New Zealand. However, the cancer risk level posed by combined direct ingestion, dermal contact, inhalation of soil particles, and inhalation of surface soil vapor met the rigorous international criteria (1 × 10(-6)). The concentration of total PAHs was (1052 ± 73) μg/kg d.w. in vegetation (mean ± standard error). The cancer risks posed by ingestion of vegetation ranged from 2×10-5 to 2 × 10(-4) with an average of 1.66 × 10(-4), which was higher than international excess lifetime risk limits for carcinogens (1 × 10(-4)). The geochemical indices indicated that the PAHs in soil and vegetables were mainly from vehicle and crude oil combustion. Both the total PAHs in vegetation and bioconcentration factor for total PAHs (the ratio of total PAHs in vegetation to total PAHs in soil) increased with increasing pH as well as decreasing sand in soil. The total variation in distribution of PAHs in vegetation explained by those in soil reached 98% in RDA, which was statistically significant based on Monte Carlo permutation. Common pollution source and notable effects of soil contamination on vegetation would result in highly similar distribution of PAHs in soil and vegetation.

Accumulation, allocation, and risk assessment of polycyclic aromatic hydrocarbons (PAHs) in soil-Brassica chinensis system

Farmland soil and leafy vegetables accumulate more polycyclic aromatic hydrocarbons (PAHs) in suburban sites. In this study, 13 sampling areas were selected from vegetable fields in the outskirts of Xi’an, the largest city in northwestern China. The similarity of PAH composition in soil and vegetation was investigated through principal components analysis and redundancy analysis (RDA), rather than discrimination of PAH congeners from various sources. The toxic equivalent quantity of PAHs in soil ranged from 7 to 202 μg/kg d.w., with an average of 41 μg/kg d.w., which exceeded the agricultural/horticultural soil acceptance criteria for New Zealand. However, the cancer risk level posed by combined direct ingestion, dermal contact, inhalation of soil particles, and inhalation of surface soil vapor met the rigorous international criteria (1×10⁻⁶). The concentration of total PAHs was (1052±73) μg/kg d.w. in vegetation (mean±standard error). The cancer risks posed by ingestion of vegetation ranged from 2×10⁻⁵ to 2×10⁻⁴ with an average of 1.66×10⁻⁴, which was higher than international excess lifetime risk limits for carcinogens (1×10⁻⁴). The geochemical indices indicated that the PAHs in soil and vegetables were mainly from vehicle and crude oil combustion. Both the total PAHs in vegetation and bioconcentration factor for total PAHs (the ratio of total PAHs in vegetation to total PAHs in soil) increased with increasing pH as well as decreasing sand in soil. The total variation in distribution of PAHs in vegetation explained by those in soil reached 98% in RDA, which was statistically significant based on Monte Carlo permutation. Common pollution source and notable effects of soil contamination on vegetation would result in highly similar distribution of PAHs in soil and vegetation.