Heavy metal concentrations and enzymatic activities in the functional zone sediments of Haizhou Bay, Lianyungang, Jiangsu, China

Pollution, risks, and sources of heavy metals in sediments from the urban rivers flowing into Haizhou Bay, China

The Haizhou Bay in eastern China, for a long time, is seriously polluted with heavy metals (HMs) due to intensive anthropic pressure. The river runoff is the dominant pathway of HM transport in the coastal region. However, the information on HM pollution in coastal rivers flowing into Haizhou Bay was still limited, and potential risks and possible sources raised by HMs in this area were neglected up to now. To fully understand the distribution and ecological risks of sediments in seven rivers along the bay, surface sediments were collected and seven HMs (Cr, Mn, Ni, Cu, Zn, Cd, and Pb) were investigated. The results showed that HM concentrations generally met the primary standard criteria of China (marine sediment quality), except for Cu and Zn. On the other hand, Zn and Cu tended to exhibit probable adverse biological effects in the Shawang River comparison with some sediment quality guidelines (SQGs). Moreover, the enrichment factor and geo-accumulation index demonstrated that there was no or slight contamination to be found for Cr, Mn, Ni, Cu, Zn, and Pb and moderate pollution for Cd. The contamination factor (C_fⁱ), integrated contamination degree (CF), modified degree of contamination (_mC_d), and modified pollution index (MPI) revealed individual metal contamination in localized areas. In these river sediments, the potential ecological risk (RI) was low to moderate, except Cd posted a considerable ecological risk because of its high enrichment. Furthermore, the Shawang River and Linhong River were seriously polluted with HMs among seven rivers. These results provided a new direction for controlling HM pollution in Haizhou Bay which suggested substantial measures should be implemented to alleviate the potential risk of HMs, to these rivers sediments.

Arsenic (As) contamination in sediments from coastal areas of China

Arsenic (As) from various anthropogenic sources has accumulated in estuarine and coastal sediments of China in the past decade, but we know little about the overall situation of As pollution at a national scale. Here, we analysed the spatial-temporal distribution characteristics, source, fate, and potential risks of As from 11 provincial-level regions across coastal China based on reviewed data extracted from previous studies published in the past 20 years. The anthropogenic contribution to As load was evident in 8 out of 11 provinces, especially in developed areas such as Tianjin, Zhejiang, and Guangdong. The weighted mean concentration of As in coastal sediments was 9.75 mg kg^-1, which was close to national agricultural land (10.7 mg kg^-1) and mixed land (12.1 mg kg^-1) soil values, and this indicated the likely terrestrial influences and homogenization of As distribution at the interface between land and sea. The accumulation has decreased significantly since 2005, which might be due to continuously reduced emissions from farming and animal husbandry and household consumption in the catchment of coastal areas. The geoaccumulation index indicated that the proportions of unpolluted, unpolluted to moderately polluted, and moderately polluted cases were 48%, 28%, and 8%, respectively. This study provides a comprehensive and quantitative review on As contamination in coastal sediments on a national scale. The results could be used in coastal sediment quality assessment and decision-making by authorities to meet the regulatory requirements linked to coastal environmental protection and management.

Source apportionment of heavy metals in sediments of the urban rivers flowing into Haizhou Bay, Eastern China: using multivariate statistical analyses and Pb-Sr isotope fingerprints

Urban river runoff carrying various anthropogenic sources of heavy metals (HMs) is the most important input pathways for HM pollutions in the coastal region, apportioning sources of environmental pollutants is key to controlling coastal HM pollution. In the study, surface sediments were collected from seven urban rivers flowing through Lianyungang City and discharging into Haizhou Bay, Eastern China. The concentrations of HMs of the river sediments were, in mg/kg (mean value ± standard deviation): Mn (550 ± 227) > Zn (67 ± 61) > Cr (33 ± 12) > Ni (21 ± 8.5) > Cu (16 ± 7.6) > Pb (15 ± 5.6) > Cd (0.11 ± 0.06), which were slightly to moderately polluted. As important outlets for municipal and industrial sewages, the Shawang River and Linhong River were the most polluted. Based on the multivariate statistical analysis, HMs were attributed to anthropogenic source (industrial, domestic, and agricultural discharges) and natural source (soil parent materials and atmospheric deposition). Based on isotope source apportionment, Pb was mainly from natural source, exhausts of leaded gasoline vehicles, and coal combustion, with the mean contributions of 39.3%, 23.7%, and 37.0%, respectively, and Sr originated from natural source and anthropogenic source, with mean contributions of 31.8% and 68.2%, respectively. Pb-Sr isotopes illustrated that anthropogenic inputs were the dominant source for HMs in urban river sediments flowing into Haizhou Bay, and the isotope tracing results make up the discriminating deficiency of the multivariate statistical analysis.

Potential of cotton for remediation of Cd-contaminated soils

The present research was conducted to study the potential of cotton for the remediation of soils contaminated with Cd, to understand the biochemical basis of its tolerance to, and to investigate the plant-microbe interaction in the rhizosphere for enhancement of phytoextraction of Cd. Cotton (Bt RCH-2) was exposed to four Cd levels (0, 50, 100, and 200 mg/kg soil) in a completely randomised design and found that the plant could tolerate up to 200 mg/kg soil. Cd stress increased the total phenol, proline, and free amino acid contents in the plant leaf tissue compared with control but inhibited basal soil respiration, fluorescein diacetate hydrolysis, and activities of several enzymes viz. dehydrogenase, phosphatases, and β-glucosidase in the soil over control. The concentration of Cd in the shoot was less than the critical concentration of 100 µg/g dry weight, and bioconcentration and translocation factors were < 1 to classify the plant as a hyperaccumulator of Cd. This was further confirmed by another experiment in which the cotton plant was exposed various higher levels of Cd (200, 400, 600, 800, and 1000 mg/kg soil). Though the concentration of Cd in the shoot was > 100 µg g ^-1dw beyond 600 mg Cd/kg soil, the bioconcentration and translocation factors were < 1. The study on plant-microbe (Aspergillus awamori) interaction revealed that the fungus did not affect the absorption of Cd by cotton. It was concluded that the cotton was classified as an excluder of Cd and therefore could be suitable for the phytostabilization of Cd-contaminated soils.

Ecological risk assessment and heavy metal contamination in the surface sediments of Haizhou Bay, China

In this study, the characteristics and spatial distribution of heavy metal pollution in the surface sediments of Haizhou Bay, one of the largest bays in China, were investigated. The potential ecological risks posed by seven heavy metals were analyzed by using the Hakanson comprehensive pollution index and geoaccumulation index (Igeo). A correlation matrix map was applied to explore the relationships between the seven heavy metals and environmental elements. The results showed that the contents of heavy metals in the southern area of Haizhou Bay are high, whereas those in the northern area are low. The results of the pollution assessment of heavy metals were largely consistent between the Igeo method and the potential ecological risk index method. The seven heavy metals ranked in descending order of potential ecological risk coefficient as follows: Hg, Cd, As, Pb, Cu, Cr and Zn. The environmental quality assessment showed that Hg is the main heavy metal pollutant in surface sediments in Haizhou Bay, and some stations have reached a high pollution level and should receive more attention.

Heavy metal contamination assessment of surface sediments of the Subei Shoal, China: Spatial distribution, source apportionment and ecological risk

This study investigated heavy metals (Ni, Zn, Cr, Cu, As, Pb, Cd and Hg) concentrations in surface sediment of Subei Shoal, China, to illustrate their spatial distribution characteristics, sources and potential ecological risk of pollution. Contents of total organic carbon (TOC), clay, silt and sand were 1.7 ± 0.8%, 3.3 ± 3.2%, 13.6 ± 14.2% and 83.1 ± 17.4%, respectively. The spatial distribution of TOC, clay and silt were similar; however, distribution of Hg was inverse. Concentrations of Ni, Zn, Cr, Cu, As, Pb, Cd and Hg were 47.88 ± 8.93, 38.18 ± 8.86, 19.22 ± 5.14, 11.32 ± 5.07, 6.97 ± 2.45, 0.13 ± 0.72, 0.56 ± 0.77 and 0.06 ± 0.02 mg kg^-1 sediment, respectively. Principal component analysis suggested that Cu, Zn, Cd, Cr and Ni were mainly derived from natural sources, whereas Pb, Cd, As and Hg from industrial and agricultural sources. Results of geo-accumulation index, potential ecological risk index (RI), pollution load index (PLI), toxic risk index (TRI) and contamination severity index (CSI) demonstrated that pollution levels of Cd and Hg were moderate, which should attract more attention as main pollution factors. The pollution was mainly distributed in the central and northern parts, and the southern part had a good ecological environment. Moreover, the contaminated stations accounted respective for 33.4%, 25.9%, 33.3% and 70.4% of RI, PLI, TRI and CSI, of which 70.4% of the contamination severity index stations contained 66.7% of much lower severity stations. These findings could contribute to more effective exploitation of tidal flat resources, and the prevention and treatment of tidal marsh environment.