Ecotoxicological risk of antibiotics and their mixtures to aquatic biota with the DGT technique in sediments.

Antibiotics are emerging contaminants and widely used in human healthcare, livestock, and aquaculture. The toxicity posed by antibiotics and their mixtures in sediments depends on their bioavailability. Now, the bioavailability of organic materials can be determined accurately by the diffusive gradients in thin films (DGT) technique. This technique was used for the first time ever in this study to evaluate in detail the integral toxicity of antibiotics in sediments to aquatic biota. Zhelin Bay was selected as a case study, because it is the largest mariculture area in eastern Guangdong, South China. Two antibiotics, chlortetracycline (CTC) (A) and sulfachlorpyridazine (SCP), were detected at average concentrations of 2.83 and 1.14 ng/ml, respectively. The other fifteen antibiotics were undetectable. The single risk assessment based on the risk quotient (RQ) of CTC and SCP shows that a relatively low risk has occurred. After this careful assessment of probabilistic ecotoxicological risks, the combined toxicity of antibiotic mixtures (CTC and SCP) clearly indicates that the toxicity probability of surface sediments to aquatic organisms was relatively low (0.23%).

Probabilistic risk assessment of microplastics on aquatic biota in coastal sediments.

As an emerging form of pollution, microplastic contamination of the coastal ecosystems is one of the world's most pressing environmental concerns. Coastal sediments have been polluted to varying degrees by microplastics, and their ubiquitous presence in sediments poses a threat to marine organisms. However, there is currently no ecological risk assessment of microplastics on aquatic biota in sediments. This study, for the first time, established a new procedure to evaluate the toxicity of microplastics on aquatic biota in sediments, based on the probabilistic risk assessment (PRA) concept. The choice of Zhelin Bay as the case study site was based on its severe pollution status. The average content of microplastics in the sediments of Zhelin Bay was 2054.17 items kg-1 dry weight, and these microplastics consisted of 46 different species. Microplastics in sediments exist in five different forms, with the film form being the main composition, and the majority of microplastics have particle sizes ranging from 100 to 500 µm. Correlation analysis (CA) reveals significant negative correlations between microplastic abundance, and Al2O3 and SiO2. The toxicity of microplastics, based on the PRA concept, suggests that Zhelin Bay surface sediments had a low probability (3.43%) of toxic effects on aquatic biota.

Distribution, Multi-Index Assessment, and Sources of Heavy Metals in Surface Sediments of Zhelin Bay, a Typical Mariculture Area in Southern China.

The occurrence, multi-index assessment, and sources of heavy metals in surface sediments of Zhelin Bay were investigated. Average heavy metal concentrations (mg/kg) were 81.89 (Cr), 770.76 (Mn), 16.81 (Co), 62.25 (Ni), 96.30 (Cu), 162.04 (Zn), and 73.40 (Pb), with the concentrations of studied seven heavy metals being significantly higher than their corresponding background values. Geo-accumulation index (Igeo) and pollution load index (PLI) were implemented to assess degree of heavy metal contamination. The Igeo and PLI indicated that Cr, Mn, Co, Zn, and Pb were slightly polluted, and Cu and Ni were moderately polluted in the region. Potential ecological risk index (RI) and mean possible effect level (PEL) quotient were conducted to assess ecological risk. The RI and mean PEL quotient demonstrated that surface sediments of Zhelin Bay were slight ecological risks and exhibited a 21% probability of toxicity. Principal component analysis (PCA) combined with the correlation analysis (CA) and hierarchical cluster analysis (HAC) revealed that the heavy metal contamination in Zhelin Bay might originate from three type sources.

Rare earth elements in sediments from a representative Chinese mariculture bay: Characterization, DGT-based bioaccessibility, and probabilistic ecological risk.

Rare earth elements (REEs) are emerging contaminants due to their worldwide exploitation in the high-technology sector. Aquaculture systems, particularly those located within coastal areas, are fragile ecosystems due to anthropogenic impacts regarding urban and aquaculture activities. However, to date, there are no reports on the combined toxicity of rare earth element (REE) mixtures on aquatic biota in sediments from coastal aquaculture systems. In this study, the combined toxicity of REE mixtures based on probabilistic risk assessment indicated that the surface sediments of Zhelin Bay had a 1.86% probability of toxic effects on aquatic biota. The average value of total REEs (TREEs) was 297.37 µg/g, with light REEs representing the major part. A factor analysis (FA)-geographic information system (GIS)-based approach coupled with correlation analysis (CA) revealed that the REEs are derived from anthropogenic sources through fluvial processes.

Risk assessment of heavy metal and pesticide mixtures in aquatic biota using the DGT technique in sediments.

Heavy metals and pesticides (HMPs) are common contaminants due to their extensive use worldwide. Diffusive gradients in thin films (DGT) are a good method for measuring the bioavailable concentration of pollutants. This study represents the first evaluation of HMP toxicity in aquatic biota using the DGT technique in sediments. Zhelin Bay was selected as the case study site because it has been contaminated by pollutants. Nonmetric multidimensional scaling (NMS) analysis reveals that a diverse range of pollutants (V, Cr, Ni, Cu, Zn, As, Se, InHg, Mo, Cd, Sb, W, Pb, CLP, PYR) are mainly influenced by sediment characteristics. Assessment of single HMP toxicity found that the risk quotient (RQ) values for Mn, Cu, inorganic Hg (InHg), chlorpyrifos (CLP) and diuron (DIU) are significantly higher than 1, indicating that the adverse effects of these single HMPs should not be ignored. The combined toxicity of HMP mixtures based on probabilistic ecotoxicological risk assessment shows that Zhelin Bay surface sediments had a medium probability (54.6%) of toxic effects to aquatic biota.

Heavy metal fractionation and ecological risk implications in the intertidal surface sediments of Zhelin Bay, South China.

Intertidal surface sediments collected from Zhelin Bay, the largest mariculture base of eastern Guangdong Province of China, were analyzed for total metal concentrations and chemical speciation. Average total metal concentrations (mg/kg) were 0.063 (Cd), 35.69 (Pb), 23.07 (Cr), 7.50 (Ni), 7.95 (Cu), 74.95 (Zn), and 751.32 (Mn). Concentrations of Cd, Cu, Zn, and Mn were significantly higher than the corresponding background values of Zhelin Bay. All studied metals were dominated by residual fractions, whereas the second relatively higher average portions of Cd (24.10%) and Mn (15.17%) were strongly associated with the acid-soluble fraction. Overall, the intertidal surface sediments of Zhelin Bay were only slightly polluted based on the pollution load index (PLI), with a 21% probability of toxicity based on the mean effects range-median quotient. The metals Cd and Mn posed medium to high risk levels based on the method of risk assessment code (RAC).

Characterization, sources, and ecological hazards of polycyclic aromatic hydrocarbons in the intertidal sediments of Zhelin Bay, the biggest mariculture area on the eastern Guangdong coast of China.

Distribution characteristics, potential sources, and possible biological hazards of polycyclic aromatic hydrocarbons (PAHs) were examined in intertidal surface sediments of Zhelin Bay, the biggest mariculture base of eastern Guangdong Province, Southern China. The total PAH concentrations ranged from 8.05-51.32 ng/g (dry weight) with an average of 29.23 ng/g, which is beneath the documented concentrations in intertidal sediments gathered from various bays across the globe. The composition of PAHs was distinguished by high molecular weight (HMW, 4-6 rings) PAHs, with phenanthrene (PHE), fluoranthene (FA), and benzo(b)fluoranthene (BbFA) established as predominant components. Principle component analysis along with multivariate linear regression discovered that liquid fossil fuel combustion and coal/wood combustion contribute to 60.23% and 39.77% of PAHs in Zhelin Bay's intertidal sediments, respectively. Overall, surface sediments of Zhelin Bay have an 8% increased incidence of adverse biological effects due to PAH contamination, based on the mean probable effect level quotient.

Sedimentary records of recent anthropogenic eutrophication and metal contamination in Zhelin Bay, an important mariculture area in Southern China.

Dinoflagellate cysts (dinocysts), biogenic elements and metals were analyzed from sediment cores collected from Zhelin Bay of the South China Sea in December 2008 to understand the environmental changes over the past 50years. Dinocyst concentrations ranged from 0cysts/g to 770cysts/g, and they were dominated by heterotrophic taxa. There was a clear increase trend upcore for biogenic elements, except for biogenic silica. Metals originated from both the lithogenic source and human activities, and significantly increased after 1985-1995. Environmental changes in the past 50years can be divided into three stages: (1) before 1985, during which biogenic elements, cyst flux and metals were low; (2) from 1985 to the early 2000s, characterized by an obvious increase of dinocysts, TOC, TN and most metals, while TOC/TN and BSi decreased; and (3) after 2000, the period of rapid increase of dinocysts, TOC and TN but decrease of certain contamination metals.

Distribution and sources of organic carbon, nitrogen and their isotopes in surface sediments from the largest mariculture zone of the eastern Guangdong coast, South China.

China is the world's largest mariculture producer. However, there is limited detailed information on organic matter distribution generated by mariculture in China. This study assessed the total organic carbon (TOC), total nitrogen (TN), and isotopic composition (δ13C and δ15N) in surface sediments from Zhelin Bay in South China. TOC, TN, δ13C and δ15N ranged from 0.46-1.23%, 0.08-0.20%, -22.07 to -21.13‰ and 5.28-7.14‰, respectively, and followed similar spatial patterns. The C/N ratio coupled with isotopic composition (δ13C and δ15N), indicates that the TOC originated from both terrestrial and marine sources. In general, surface sediments of Zhelin Bay were dominated by marine derived organic carbon; this form of carbon was separately calculated based on δ13C-based two end-member mixing and C/N ratio models.

Polycyclic aromatic hydrocarbons (PAHs) in sediments of Zhelin Bay, the largest mariculture base on the eastern Guangdong coast, South China: Characterization and risk implications.

We investigated distribution, sources, and potential risks of polycyclic aromatic hydrocarbons (PAHs) in the surface sediments from the largest mariculture base in the eastern part of the province of Guangdong in southern China. Total concentrations of ∑PAHs were 29.38-815.46ng/g (dry weight), with a mean of 421.48ng/g. The composition of PAHs was characterized by an abundance of low molecular weight PAHs (2-3 benzenoid ring), and Phenanthrene (PHE), Anthracene (AN) and Fluoranthene (FA) were the predominant constituents. PAHs in this area appear to have mainly originated from petroleum sources and the combustion of grass, wood, and coal. PAHs in surface sediments of Zhelin Bay had a 9% incidence of causing adverse biological effects on aquatic organisms, according to the mean effects range-median quotient.

[Distribution Characteristics and Ecological Risk Assessment of Organochlorine Pesticides in Surface Sediments of Zhelin Bay in Guangdong Province, China].

The distribution characteristics and pollution degrees of 20 organochlorine pesticides (OCPs) were investigated in surface sediments from Zhelin Bay south of China and the ecological risk of OCPs and integrated ecological risk at the samples stations in sediments were evaluated by risk quotient (RQ) and sediment quality guideline of NOAA. The possible sources of HCHs and DDTs in sediments were preliminarily studied, and the correlation between OCPs and sediment characteristic parameters was discussed. The concentrations of DDTs in surface sediments were found to be higher than those of other OCPs, especially p,p'-DDD, and the concentrations of DDTs were higher than the limited values of Chinese Marine sediment quality criteria. The total concentration of 20 OCPs in surface sediments ranged from 14.14 to 306.88 ng·g-1, with a mean concentration of 78.37 ng·g-1, and the highest total concentration was at site 8(S8). There were inevitable adverse biological effects and high ecological risk of p,p'-DDD and p,p'-DDT, high integrated ecological risk at S8 and S10. The possible sources of HCHs in surface sediments of Zhelin Bay were mainly from the application of Lindane pesticides. At S1,S2,S10,S11 there was input of DDT into mariculture area of Zhelin Bay, and at the other sites the sources of DDT were from the early residue in sediments or the long-term weathering sediments of using pesticides. There was a very significant positive correlation between HCHs, endosulfan, chlordane and dieldrin in sediments, while there was a negative relation between the above OCPs and TOC, which indicated that the presence of TOC could promote their biodegradation. There was a significant positive correlation between p, p'-DDD and Ca, which revealed that DDT used in the early period was deposited with biological carbonate. Increasing size of sediment particles discouraged the accumulation and enrichment of OCPs in sediments.

Metal pollution status in Zhelin Bay surface sediments inferred from a sequential extraction technique, South China Sea.

Surface sediments collected from Zhelin Bay, the largest mariculture base of eastern Guangdong Province, were analyzed for total metal concentrations and chemical speciation. The results demonstrated that the average total concentration (mg/kg) ranges were 36.7-65.8 (Pb), 53.8-98.8 (Cr), 39.0-87.1 (Ni), 50.9-144.5 (Cu), and 175.0-251.2 (Zn), which were clearly higher with respect to their corresponding benchmark values. The predominant speciation of Pb was reducible and comprised a residual fraction, whereas a major portion (57.6-95.4%) of Cr, Ni, Cu, and Zn was strongly associated with the residual fractions. Taking as a whole, surface sediments of Zhelin Bay had a 21% probability of toxicity based on the mean effects range-median quotient.