Application of diffusive gradients in thin films to determine rare earth elements in surface sediments of Daya Bay, China: Occurrence, distribution and ecotoxicological risks.

Known as burgeoning contaminants, the bioavailability of rare earth elements (REEs) can be determined using diffusive gradients in thin films (DGT). As Daya Bay (South China) has been under serious anthropogenic influences, the present study examined the distribution of REEs in surface sediments and their possible ecological risks in the bay. The range of DGT-labile concentrations of REEs (∑REEs) was from 5.67 µg/L to 8.41 µg/L, with an average of 7.34 µg/L. Results of assessment of single REE toxicity revealed that the risk quotient (RQ) values of Y, Ce and Yb were >1, indicating that their potential negative impacts on the nearby environment. However, analysis of the integral toxicity of REE mixtures through assessment of probabilistic ecotoxicological risks showed that there was a negligibly low probability of toxicity of PRE surface sediments to aquatic organisms in the study area.

Rising temperature contributed to the outbreak of a macrozooplankton Creseis acicula by enhancing its feeding and assimilation for algal food nearby the coastal Daya Bay Nuclear Power Plant.

An outbreak of a macrozooplankton Creseis acicula occurred in the summer of 2020 nearby the Daya Bay Nuclear Power Plant located on the coast of the Daya Bay in the South China Sea. The outbreaks of C. acicula often threaten human health, the marine environment, and other human activities including the safe operation of coastal nuclear power plants. Seawater temperature has been suggested as an important factor influencing such outbreaks. However, the underlying mechanisms through which temperature influences C. acicula remains unknown. Here, we studied the effects of temperature on the ingestion and assimilation of algal food by feeding radiocarbon-labeled algae Chlorella sp. at simulated field temperatures (19-31 °C) to C. acicula collected during the outbreak in the Daya Bay. We also quantified the allocation of the food carbon to dissolved organic carbon (DOC), CO2, and fecal pellets. The results showed that the zooplankton during the same feeding time ingested doubled or tripled algal food at higher temperatures, and it produced and released significantly more DOC, CO2, and fecal pellets with more ingested food carbon. Meanwhile, the assimilation efficiency for the ingested food carbon slightly increased from 48% to 54% with rising temperature. As a result, higher assimilation rates indicating faster growth of C. acicula were observed at higher temperatures. In addition, the high activation energy of 0.908 eV indicated that the assimilation rate was very sensitive to temperature rising. Our results show that relatively rising temperature can enhance C. acicula's ingestion and assimilation rates for algal food, benefit its growth and metabolism, and contribute to its outbreak. This study provides a mechanistic interpretation for the relationship between rising temperature and the outbreaks of C. acicula and suggests that such outbreaks may occur more frequently and widely in the warming ocean.

Appraising ecotoxicological risk of mercury species and their mixtures in sediments to aquatic biota using diffusive gradients in thin films (DGT).

Mercury (Hg) is a global, persistent and inevitable pollutant, the toxicity of which is mostly reflected in its species including inorganic Hg (InHg) and methyl mercury (MeHg). Using diffusive gradients in thin films (DGT) is deemed as a reliable technique to determine the bioavailability of pollutants. This study is the first attempt to assess the integrated toxicity of mercury species mixtures in sediments to the aquatic biota based on the DGT technique. In the course, the Daya Bay under serious anthropogenic influences was selected as the study case. The results showed that the DGT concentrations of InHg and MeHg were detected as 0.30-1.93 µg/L and 0.28-1.94 µg/L respectively in the surface sediments collected from the Daya Bay. In terms of the toxicity of single mercury species, the risk quotient (RQ) values of InHg and MeHg significantly exceeded 1, indicating that the adverse effects of InHg and MeHg should not be ignored. In terms of the integrated toxicity of mercury species mixtures, the probabilistic biological risk assessment results demonstrate that Daya Bay features low (3.32%) probability of toxic effects in its surface sediments to the aquatic biota.

Polycyclic Aromatic Hydrocarbons (PAHs) in the intertidal sediments of Pearl River Estuary: Characterization, source diagnostics, and ecological risk assessment.

The surface intertidal sediments in the Pearl River Estuary of China were analyzed from multiple perspectives, including the distribution characteristics, potential sources, and biological risks of polycyclic aromatic hydrocarbons (PAHs). The average concentration of PAHs, ranging from 73.68 ng/g to 933.25 ng/g, was 346.78 ng/g. PAHs are mainly composed of the 2- and 3-ring PAHs, with naphthalene (Nap), phenanthrene (Phe), pyrene (Pyr), benzo(g,h, i) perylene (Dib), fluoranthene (Flua), and indeno (1,2,3-c,d) pyrene (Ind) as the dominant constituents. The principal component analysis combined with multiple linear regression showed that petroleum combustion and biomass/coal combustion have contributed 52.78% and 40.53%, respectively, to the PAHs in intertidal sediments of Pearl River Estuary. The occurrence of adverse biological effects as a result of PAH contamination in the intertidal sediments of Pearl River Estuary has increased by 8% based on the mean value of the probable effect quotient.

Non-metric multidimensional scaling and human risks of heavy metal concentrations in wild marine organisms from the Maowei Sea, the Beibu Gulf, South China Sea.

We investigated heavy metal concentrations in wild marine organisms from Maowei Sea, a significant gulf of low-latitude developing regions of the Beibu Gulf, South China Sea. Twenty species, comprising fish, cephalopods, and crustaceans were collected and analyzed for heavy metals. Heavy metal levels (mg/kg, wet weight) in the aquatic organism samples were: 0.003-1.800 for Cd, 0.02-0.14 for Pb, 0.10-0.63 for Cr, 0.20-77.50 for Cu, 9.50-64.60 for Zn, 0.006-0.066 for Hg, and 0.10-1.50 for As. Non-metric multidimensional scaling coupled with cluster analysis revealed two groupings that mainly resulted from different species of the metals in marine organisms. The highest concentrations of Cd, Pb, Cr, Ni, Cu, Zn, Hg, and As were found in species of cephalopods. Health risk assessment based on the target hazard quotients (THQ) and total THQ indicated no significant adverse health effects from consumption of marine organisms.

[Characteristics of net phytoplankton community and their relationships to environmental factors in the waters around Nansha Islands].

Based on samples collected in the waters around Nansha Islands from August 25 to September 28, 2011, the characteristics of net phytoplankton community and their relationships to environmental factors were investigated. A total of 113 species, belonging to 34 genera of 3 phyla were identified, among which 57.5% belonged to Pyrrophyta and 40.7% belonged to Bacillariophyta. Ceratium in Pyrrophyta had the most species accounting for 30.1% of the 113 species. The average abundance of net phytoplankton was 2.12 x 10(4) cell x m(-3) and high abundances were encountered in the complex gyre adjacent to Reed Tablemount and in the Cyclonic Gyre adjacent to Wan'an Tan. Trichodesmium in Cyanophyta was the dominant functional group, taking up 77.0% of the total net phytoplankton abundance. Trichodesmium thiebautii, T. erythraeum and Pyrocystis noctiluca were the major dominant species. The dominant species varied with locations. Cyanophyta widely dominated at stations 3, 5, 6 and 10-14, Pyrrophyta were the dominant phytoplankton in the central locations at stations 4 and 7-9, while Bacillariophyta dominated only at the southernmost stations 1 and 2. The values of Shannon index and Pielou evenness index of net phytoplankton community were 3.10 and 0.62, respectively. The salinity, water temperature, contents of ammonium, nitrite, phosphate and silicate, as well as mesoscale gyres and the west Nansha coastal current were the important environmental factors affecting the characteristics of net phytoplankton community. The ordination plots by canonical correspondence analysis could well display the characteristics of net phytoplankton community and their relationships to environmental factors.