Adsorption of metals on aged microplastics in intensive mariculture areas: Aggravating the potential ecological risks to marine organisms.

Field determination of the metal adsorption capacity of microplastics (MPs) by using a passive sampler had been done in typical subtropical mariculture area in China. The adsorption of eight metals (Fe, Mn, Cu, Zn, As, Pb, Cr and Cd) by five types of MPs (low-density polyethylene, polypropylene, polystyrene, poly(ethylene terephthalate) and poly(vinyl chloride) (PVC) was compared, including metal types, mariculture types (cage and longline culture), metal residue content in ambient environment, polymer types and particle sizes of MPs. The results showed that Cu, Zn, As, Cd, Pb and Cr in the mariculture environment were contaminated compared with the quality criteria. The concentrations of these six metals adsorbed on five MPs increased linearly with those in seawater. More enriched Cu and As in MPs in marine cage culture than in longline culture, due to the obvious endogenous pollution emissions for the artificial diets, fish medicine and disinfectants. Aged PVC with more cracks and pores showed higher metal adsorption capacity than any other polymers. MPs with a smaller size range of 50-74 µm tended to accumulate higher amounts of metals than those with a larger size range of 74-178 µm, consisting with the surface characteristics of MPs. The significant positive relationship between the concentrations of nutrients in seawater and the adsorption amounts of Cu, Zn and As on MPs implies that the eutrophication would promote their pollution. Based on the ecological risk assessment, the occurrence of MPs could aggravate the potential risk of metals to marine organisms in intensive mariculture areas. This is the first time to reveal the impacts of the adsorption of metals on aged MPs on the potential ecological risks of metals to organisms under the realistic environmental condition.

Occurrence, vertical distribution and transport of organic amine pesticides in the seawater from the East China Sea and the South China Sea.

Organic amine pesticides (OAPs) are widely used as insecticides, fungicides and herbicides in agricultural production. China is a large agricultural country, and the sprayed pesticides may impact the fragile marine environment through surface runoff. This study revealed the pollution characteristics of thirty-three OAPs in the East China Sea (ECS) and the South China Sea (SCS) and investigated their vertical variations in water columns. The ∑OAPs ranged from below method detection limits to 3.4 ng/ L, with an average value of 0.93 ng/ L. Diphenylamine and beflubutamid were the two most abundant compounds, contributing 64 % and 14 % of the ∑OAPs, respectively. The ∑OAPs in the ECS were significantly (M-W U test, p < 0.01) higher than that in the SCS, and OAPs exhibited different composition profiles. Diphenylamine was the most abundant compound in the ECS, while beflubutamid was dominant in the SCS, which may be related to industrial production (such as rubber synthesis) and agricultural activities. In the water columns, OAPs concentrations were higher in deep layers compared to that in surface seawater, which may be due to weak light and low temperature reducing the degradation of pesticides, indicating the deep ocean is a sink for OAPs. Under the dilution of seawater, the concentrations of OAPs decreased from the Pearl River Estuary to the open sea, and the South China Sea Warm Current also caused the decrease of OAPs from south to north. A preliminary risk assessment indicated that OAPs in the water pose no significant risk to aquatic organisms.

Selective adsorption of antibiotics on aged microplastics originating from mariculture benefits the colonization of opportunistic pathogenic bacteria.

Microplastics and antibiotics widely coexist in the aquatic environment, especially in mariculture regions. However, antibiotics adsorbed on microplastics and their role in the colonization of microorganisms on microplastics are poorly understood. Therefore, in-situ aging experiments were conducted to investigate the impact of antibiotics and microplastics co-occurrence on microorganisms and assess their potential risks to human health. Results showed that antibiotics were adsorbed selectively on microplastics, with 29 investigated antibiotics (n = 40) detected in surrounding water but only 6 investigated antibiotics were adsorbed on microplastics. The concentration of antibiotics accumulated on microplastics was controlled by microplastic types and environmental conditions. For example, aged polypropylene (PP) had more developed pore structures resulting in higher adsorption of antibiotics than other microplastic types. High-throughput sequencing showed higher diversity and distinct composition of microorganisms attached to the microplastics than the surrounding water. Opportunistic pathogenic bacteria such as Mycobacterium possessed positive relationships with tetracycline and doxycycline on aged microplastics, which showed adsorbed antibiotics on aged microplastics could benefit some specific pathogens colonized on the microplastics and spread into unaffected ecosystems, marine organisms even humans. The health risk quotient (HQ) implied the potential human health risk of consuming commercial seafood polluted by antibiotics and microplastic loaded with antibiotics. This study revealed the interaction of antibiotics and microorganisms with aged microplastics in aquaculture systems, providing a novel insight into their synergistic effects on ecological and human health.

Dissolved PAHs impacted by air-sea interactions: Net volatilization and strong surface current transport in the Eastern Indian Ocean.

In the Indian Ocean, the marine fate of polycyclic aromatic hydrocarbons (PAHs) is impacted by the unique air-sea interactions with great monsoon characters. By collecting water-column samples during the monsoon transition period, we found PAHs (∑8PAH: 1.1-27 ng L-1) showed significantly different distributions from the Bay of Bengal, Equatorial Indian Ocean, Eastern Indian Ocean, and the South China Sea (p < 0.001). Their vertical profiles showed natural logarithm relationships with depth in the Bay of Bengal and Equatorial Indian Ocean. PAHs were mainly from wood/coal combustion and vehicle emission. The estimation of PAHs' air-seawater exchange flux revealed net volatilizations from seawater except in the Eastern Indian Ocean. The Wyrtki Jet, a surface current driven by the westerly wind, was observed in the equatorial area. This swift current could transport PAHs eastward efficiently with a mass flux of 636 ± 188 g s-1. The subsurface current, Equatorial Undercurrent, played a less crucial role in PAHs' lateral transport with a flux of 115 ± 31.3 g s-1. This study preliminarily revealed the role of air-sea interactions on PAHs' transport and fate in the open ocean. The coupled air-sea interactions with biogeochemical processes should be considered in future work.

Improved source apportionment of PAHs and Pb by integrating Pb stable isotopes and positive matrix factorization application (PAHs): A historical record case study from the northern South China Sea.

To obtain the historical changes of pyrogenic sources, integrated source apportionment methods, which include PAH compositions, diagnostic ratios (DRs), Pb isotopic ratios, and positive matrix factorization (PMF) model, were developed and applied in sediments of the northern South China Sea. These methods provided a gradually clear picture of energy structural change. Spatially, Σ15PAH (11.3 to 95.5ng/g) and Pb (10.2 to 74.6µg/g) generally exhibited decreasing concentration gradient offshore; while the highest levels of PAHs and Pb were observed near the southern Taiwan Strait, which may be induced by accumulation of different fluvial input. Historical records of pollutants followed closely with the economic development of China, with fast growth of Σ15PAH and Pb occurring since the 1980s and 1990s, respectively. The phasing-out of leaded gasoline in China was captured with a sharp decrease of Pb after the mid-1990s. PAHs and Pb correlated well with TOC and clay content for core sediments, which was not observed for surface sediments. There was an up-core increase of high molecular PAH proportions. Coal and biomass burning were then qualitatively identified as the major sources of PAHs with DRs. Furthermore, shift toward less radiogenic signatures of Pb isotopic ratios after 1900 revealed the start and growing importance of industrial sources. Finally, a greater separation and quantification of various input was achieved by a three-factor PMF model, which made it clear that biomass burning, coal combustion, and vehicle emissions accounted for 40±20%, 41±13%, and 19±12% of PAHs through the core. Biomass and coal combustion acted as major sources before 2000, while contributions from vehicle emission soared thereafter. The integrated multi-methodologies here improved the source apportionment by reducing biases with a step-down and cross-validation perspective, which could be similarly applied to other aquatic systems.

Environmental and Ecological Risk Assessment of Trace Metal Contamination in Mangrove Ecosystems: A Case from Zhangjiangkou Mangrove National Nature Reserve, China.

Zhangjiangkou Mangrove National Nature Reserve is a subtropical wetland ecosystem in southeast coast of China, which is of dense population and rapid development. The concentrations, sources, and pollution assessment of trace metals (Cu, Cd, Pb, Cr, Zn, As, and Hg) in surface sediment from 29 sites and the biota specimen were investigated for better ecological risk assessment and environmental management. The ranges of trace metals in mg/kg sediment were as follows: Cu (10.79-26.66), Cd (0.03-0.19), Pb (36.71-59.86), Cr (9.67-134.51), Zn (119.69-157.84), As (15.65-31.60), and Hg (0.00-0.08). The sequences of the bioaccumulation of studied metals are Zn > Cu > As > Cr > Pb > Cd > Hg with few exceptions. Cluster analysis and principal component analysis revealed that the trace metals in the studied area mainly derived from anthropogenic activities, such as industrial effluents, agricultural waste, and domestic sewage. Pollution load index and geoaccumulation index were calculated for trace metals in surface sediments, which indicated unpolluted status in general except Pb, Cr, and As.