Concentrations of PCBs in coastal mangrove sediments of Hong Kong

Distribution of microbial taxa and genes degrading halogenated organic pollutants in the mangroves

Anthropogenic activities have led to serious contamination of halogenated organic pollutants (HOPs), such as PCBs, PBDEs, and HBCDs, in the mangrove wetland. Biodegradation of HOPs is generally driven by environmental microorganisms harboring dehalogenase genes. However, little is known if HOPs can affect the distributions of HOPs-degrading bacteria and dehalogenase genes in the mangrove wetlands. Historical data suggested that HOPs contamination has been persistent and even deteriorated in the mangrove wetlands in China. We found that the organohalides-respiring bacteria Dehalococcoidia and reductive dehalogenase genes were more prevalent in the subsurface layer sediments (20-30 cm depth; 1.935-9.876 % relative abundance; 71-286 contigs) than the surface layer (0-5 cm depth; 0.174-2.020 % relative abundance; 7-130 contigs). While the genes of haloacid and haloalkane dehalogenases were more abundant in the surface layer (30-100 and 18-138 contigs) than the subsurface layer (22-56 and 50-101 contigs). The abundance of HOPs-degrading genes of reductive dehalogenase, haloacid dehalogenases, AtzA, AtzB, TrzA, TrzN, PcpB, were determined by GeoChip 5.0. Their total abundance ranged from 444.760 to 880.909. Their distributions were mainly associated with the contamination levels of HOPs and strength of anthropogenic activities around the mangrove wetlands. Therefore, the distribution of bacterial taxa and genes involved in HOPs degradation was related to the depth of sediments and affected by the selective stress from HOPs.

A novel coupled framework for detecting hotspots of methane emission from the vulnerable Indian Sundarban mangrove ecosystem using data-driven models

Coastal mangroves have been lost to deforestation for anthropogenic activities such as agriculture over the past two decades. The genesis of methane (CH₄), a significant greenhouse gas (GHG) with a high potential for global warming, occurs through these mangrove beds. The mangrove forests in the Indian Sundarban deltaic region were studied for pre-monsoonal and post-monsoonal variations of CH₄ emission. Considering the importance of CH₄ emission, a process-based spatiotemporal (PBS) and an analytical neural network (ANN) model were proposed and used to estimate the amount of CH₄ emission from different land use land cover classes (LULC) of mangroves. The field work was performed in 2020, and gas samples of various LULC were directly collected from the mangrove bed using the enclosed box chamber method. Historical climatic data (1960-1989) were used to predict future climate scenarios and associated CH₄ emissions. The analysis and estimation activities were carried out utilizing satellite images from the pre-monsoonal and post-monsoonal seasons of the same year. The study revealed that pre-monsoonal CH₄ emission was higher in the south-west and northern parts of the deforested mangrove of the Indian Sundarban. A sensitivity study of the anticipated models was conducted using a variety of environmental input parameters and related main field observations. The measured precision area under curve of receiver operating characteristics was 0.753 for PBS and 0.718 for ANN models, respectively. The temperature factor (T_f) was the most crucial variable for CH₄ emissions. Based on the PBS model with coupled model intercomparison project-6 temperature data, a global circulation model was run to predict increasing CH₄ emissions up to 2100. The model revealed that the agricultural lands were the prime emitters of CH₄ in the Sundarban mangrove ecosystem.

Distribution, Sources and Risk Assessment of Polychlorinated Biphenyls in Sediments from Beiluo River

The distribution and source of polychlorinated biphenyls (PCBs) pollution in the Beiluo River, the secondary tributary of the Yellow River, still remain unclear. With the purpose of determining the distribution, origins, and pollution levels of PCBs and their consequences on ecological risks, the concentrations of 27 PCBs at 17 locations in the sediments of the Beiluo River were examined in this study. The results showed that the mass concentrations of ∑PCBs in the sediment ranged from 0.12 to 1.25 ng∙g^-1 (DW), with the highest point at sampling site B13 downstream of the river. Compared to most river sediments, both domestically and internationally, the concentration of PCBs in the sediment of the Beiluo River was at a low level, with 10-PCB and 6-PCB as the main components, indicating that the PCBs that are difficult to volatilise and degrade are more likely to remain in the sediment. The origins of PCBs in the sediments of the Beiluo River were examined by using positive matrix factorisation (PMF). The results revealed that the contamination of PCBs in the sediments of the Beiluo River mainly resulted from industrial emissions, technical PCB mixtures, and coal and wood combustion. The results of the ecological risk assessment indicated that PCBs in the sediments of the study area rarely contribute to adverse biological effects and the potential low risk to the environment.

Investigating mangrove-human health relationships: A review of recently reported physiological benefits

Ecosystems continue to experience degradation worldwide, with diminishing ecosystem services presenting unfavourable outlooks for all aspects of human wellbeing including health. To inform protective policies that safeguard both ecological and health benefits, syntheses of available knowledge are required especially for neglected ecosystems such as mangroves. However, reviews about relationships between mangroves and human health are rare. This review identifies and categorizes evidence reported in the Web of Science database about health impacts of mangrove ecosystem goods and services. 96 papers were retained after application of exclusion criteria and filtration steps to results of database and bibliographical searches. Findings highlight most abundantly that bioactive extracts of mangrove sediment, plant, and plant associates are useful for the treatment of human ailments and infections. Also reported is the heavy and trace metal bioremediation capacity of mangroves ecosystems, with concomitant modulating effects on associated human health risks. Evidence of mangrove influence on human nutrition via fisheries and food production support services, either singularly or in conjunction with linked ecosystems is also offered. Finally, mangrove effects on the prevalence of causative agents, and therefore on the incidence and distribution of infectious diseases, are also presented. Positive influences of mangroves on human health are implied via three of the four routes reported, which diminish with degradation and appreciate with proper ecosystem functioning. The undesirable links lie chiefly with higher infectious disease risk posed by mangroves, which requires further exploration regarding suspected ecological pathways available for limiting said risks. Other gaps identified are sparse information about in-vivo efficacy and safety of mangrove bioactive isolates, specific nutrient content and diversity associated with mangrove-supported food production outcomes, and the geographically limited nature of most findings. Beyond economic value, health benefits of mangroves are significant and outweigh their disservices to humans. To ensure sustainable supply of the full complement of these benefits, they should be considered when designing ecosystems management regimes.

Polycyclic aromatic hydrocarbons (PAHs) in mangrove ecosystems: A review

Polycyclic aromatic hydrocarbons (PAHs) are organic pollutants of increasing concern in the different fields of the environment and human health. There are 16 of them that are recognized as priority pollutants by the US environmental protection agency due to their mutagenic and carcinogenic potentials. Due to their hydrophobicity and stability, they are persistent in the environment and can be transported over long distances. Their toxicological effects on multiple species, including humans, as well as their bioaccumulation in the food web became major topics in organic pollutants research this last decade. In the environment, multiple studies have been conducted on their accumulation in the soil and their degradation processes resulting in numerous review papers. However, the dynamics of PAHs in mangrove ecosystems is not yet completely understood. In this review paper, an exhaustive presentation of what is known about PAHs and their transfer, accumulation, and degradation in mangrove ecosystems is offered. This article brings to light the knowledge already acquired on the subject and the perspective research necessary to fully comprehend PAHs dynamics in mangrove ecosystems.

Occurrence of polychlorinated biphenyls (PCBs) in the sea anemone Bunodosoma zamponii, sediments and seawater from the southwestern Atlantic

Polychlorinated biphenyls (PCBs) are persistent and bioaccumulable organic compounds. The occurrence of PCBs was assessed in two populations of the intertidal sea anemone Bunodosoma zamponii living under different anthropogenic strains. One location was in vicinity to a wastewater plant (Las Delicias, LD), and the other was a preserved location chosen as a reference site (Punta Cantera, PC). Anemone populations were sampled 4 times (spring, summer, autumn and winter) throughout a year, in addition to seawater and sediment from those areas. PCB loadings ranged from 2.89 to 79.41 ng L^-1 in seawater samples and from 0.07 to 6.61 ng g^-1 dry weight in sediment samples. Total PCB levels ranged from 0.22 to 14.94 and 2.79 to 24.69 ng g^-1 wet weight in anemones from PC and LD, respectively. PCBs concentrations in anemones from LD were significantly greater than PC during spring, summer and winter. The congeners 18 and 44 prevailed in seawater samples, 44 and 52 in sediment and 18 and 132+153 in anemones. Redundancy analysis integrated PCB levels from all matrixes and bolstered contrast between sampling sites. Seasonality was also a relevant factor since during winter PCB loading was greater in sediment and anemone samples, coincident with the rainiest season. Disparity between sites could be due to LD's proximity to the wastewater plant, effect of littoral drift direction and/or asymmetries in anemones physiological condition.

Ultrasound-assisted soil washing processes using organic solvents for the remediation of PCBs-contaminated soils

Ultrasonic soil washing processes using organic solvents were investigated for the development of novel remediation technologies for persistent organic pollutants (POPs)- contaminated soils. Aluminum foil erosion was first tested to understand sonophysical activity in water, methanol (polar) and n-hexane (nonpolar) in a 28 kHz double-bath-type sonoreactor. Significant sonophysical damage on the aluminum foil was observed at the antinodes for all solvents, and the order of degree of sonophysical damage was as follows: water > methanol > n-hexane. Subsequently, conventional (mechanical mixing only) and ultrasonic soil washing (mechanical mixing and ultrasound) techniques were compared for the removal of polychlorinated biphenyls (PCBs) from soil. Two types of contaminated soils, fresh (Soil A, C0 = 2.5 mg/kg) and weathered (Soil B, C0 = 0.5 mg/kg), were used and the applied soil-to-liquid (S:L) ratio was 1:5 and 1:10 for methanol and n-hexane, respectively. The polar solvent significantly increased washing efficiencies compared to the nonpolar solvent, despite the nonpolar nature of the PCBs. Washing efficiency was significantly enhanced in ultrasonic soil washing compared to conventional washing, owing to macro- and micro-scale sonophysical actions. The highest washing efficiencies of 90% for Soil A and 70% for Soil B were observed in the ultrasonic washing processes using methanol. Additionally, a single operation of the ultrasonic washing process was superior to two sequential processes with conventional mixing in terms of washing efficiency, consumption of washing agents, treatment of washing leachate, and operation time. Finally, the removal of PCBs in an organic solvent (methanol) was investigated in photolytic and sonolytic processes for the post-treatment of soil washing leachate. A photolysis efficiency of 80% was obtained within 60 min of UV exposure for intensities of 1.0, 2.0, and 4.0 W/cm2. The primary mechanism of PCBs degradation is photolytic dechlorination. In contrast, no degradation was detected in the sonolytic process, as the excess organic solvent acted as a strong radical scavenger.

Persistent organic pollutants in sediments of the Wouri Estuary Mangrove, Cameroon: Levels, patterns and ecotoxicological significance

The anthropogenic impact in the Wouri Estuary Mangrove located in the rapidly developing urban area of Douala, Cameroon, Africa, was studied. A set of 45 Persistent Organic Pollutant were analysed in surficial mangrove sediments at 21 stations. Chlorinated Pesticides (CLPs), Polychlorinated Biphenyls (PCBs) and Polycyclic Aromatic Hydrocarbons (PAHs) have concentrations ranging from 2.2 - 27.4, and 83 - 544 ng/g, respectively. The most abundant CLPs were endosulfan, alachlor, heptachlor, lindane (γ-HCH) and DDT, which metabolites pattern revealed recent use. Selected PAHs diagnostic ratios show pyrolytic input predominantly. The sum of 7 carcinogenic PAHs (ΣC-PAHs) represented 30 to 50% of Total PAHs (TPAHs). According to effect-based sediment quality guidelines, the studied POPs levels imply low to moderate predictive biological toxicity. This study contributes to depict how far water resources are shifting within what is now termed the Anthropocene due to increasing local pressures in developing countries or African countries.

Contamination of polybrominated diphenyl ethers (PBDEs) in watershed sediments and plants adjacent to e-waste sites

Polybrominated diphenyl ethers (PBDEs) are one of the persistent toxic organic pollutants in watersheds near electrical and electronic waste (e-waste) sites (EWS). Spatial redistribution, translocation and bioaccumulation of PBDEs in natural sediment-plant ecosystems, however, are still unclear. The contamination and distribution of PBDEs in core sediments and wetland plants from two EWS and two mangrove forest sites (MFS) were investigated. The eight PBDE congeners were all detected in plant tissue and sediment samples, indicating PBDE contamination was common and severe, and their spatial variations were significant. Although sediments from EWS had higher PBDE concentrations than those in MFS, with an extremely high value of 36392 ± 5992 ng g^-1 dw, mangroves could be the sink of PBDEs, as high concentrations (327 ± 48 ng g^-1 dw) were also detected in mangrove sediments. The historical usage of PBDEs was reflected by their distribution in mangrove sediment core but not so in e-waste sediment core. PBDEs were taken up and accumulated in six wetland plants, with more accumulation in mangrove plants. These results demonstrated that PBDEs were not only contaminated in sediments adjacent to e-waste sites but also plant tissues. PBDEs could enter other environments via plant littering and/or herbivorous processes that must not be neglected.

Leaf Enzyme and Plant Productivity Responses to Environmental Stress Associated with Sea Level Rise in Two Asian Mangrove Species

As the only forests situated at the transition between land and sea, mangrove forests are one of the first ecosystems vulnerable to rising sea levels. When the sea level rises, plants are exposed to increased salinity, as well as tidal flooding. The responses of mangrove forests to changing sea levels depend on the synergistic effects of tidal flooding and salinity on plants, especially seedlings. The focus of this paper is to assess the ability of different tide position on mangrove Aegiceras corniculatum (A. corniculatum) and Bruguiera sexangula (B. sexangula) seedlings to withstand tidal flooding and seawater salinity, and to investigate the effects of tidal flooding and salinity on plant growth. To accomplish this, a controlled experiment was initiated to examine the synergistic effects of tidal flooding and salinity on the growth and physiology of A. corniculatum and B. sexangula seedlings subjected to four tidal flooding times and four levels of salinity over a course of six months. The results showed that the biomass and antioxidant enzymes of A. corniculatum and B. sexangula seedlings were significantly affected by the increase in salinity and flooding time. Changes in biomass, SOD, and CAT activity of A. corniculatum seedlings show that they are more adapted to grow in an environment with high salinity and long flooding time than B. sexangula. Our results show that species growing in middle- to low-tide levels were better adapted to sea level rise than those growing at high-tide levels.

Bioaccumulation and cycling of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in three mangrove reserves of south China

Total 22 organochlorine pesticides (OCPs) compounds and 31 polychlorinated biphenyls (PCBs) congeners in mangrove sediments and tissues (leaf, branch, root and fruit) of nine species from three Mangrove Reserves of China were studied. The mean concentrations of total DDTs, HCHs, OCPs and PCBs in sediments were 2.84, 0.06, 3.84 and 0.17 ng g^-1 dw, while those in tissues were 1.85, 0.22, 9.43 and 1.61 ng g^-1 dw, respectively. The elevated OCPs and PCBs levels in mangrove leaves may be caused by atmospheric sedimentation. The biota sediment accumulation factor (BSAF) values of both OCPs (mean: 3.4) and PCBs (mean: 9.9) are generally larger than one, implying mangroves' bioaccumulation and their ability to intercept pollutants. The BSAFs of PCBs in mangrove tissues were negatively correlated with the PCB congener's octanol-water partition coefficients (K_OW, R = 0.58, n = 31, p < 0.001), suggesting that lower chlorinated CB congeners are more bioaccumulative in mangroves. In order to better understanding the fate of these organochlorine compounds, the cycling (including the standing accumulation, the annual absorption, the annual net retention, the annual return, and the turnover period) of OCPs and PCBs in the Mangrove Reserves were estimated, and the results indicated that mangroves are playing important roles in retaining OCPs and PCBs.

Antioxidative response of Kandelia obovata, a true mangrove species, to polybrominated diphenyl ethers (BDE-99 and BDE-209) during germination and early growth

A 3-months microcosm experiment with mangrove sediment spiked with PBDEs and planted with propagules of Kandelia obovata was conducted to investigate PBDE toxicity and antioxidative responses of the germinated seedlings. BDE-99 suppressed germination rate, leaves formation and growth of mangrove seedlings. The leaves and roots of BDE-99 treated seedlings had significantly higher superoxide (O₂^-) release, malondialdehyde (MDA) and total polyphenol (TP) content, and peroxidase (POD) activity than the control. BDE-209 increased activities of all three antioxidative enzymes, catalase (CAT), POD and superoxide dismutase (SOD) in roots, but in leaves, only CAT activity was stimulated. The MDA content of BDE-209 treated seedlings was less than the control. PBDEs were found in plant tissues of the treated seedlings. These results indicated that even though PBDEs were taken up in tissues, K. obovata, due to its antioxidative defense enzymes, could tolerate PBDEs and could be used for the bioremediation of PBDE-contaminated environments.

Distribution and accumulation of mercury and copper in mangrove sediments in Shenzhen, the world's most rapid urbanized city

To investigate the influence of mangrove forest on heavy metal accumulation and storage in intertidal sediments, core sediments from natural mangrove, restored mangrove, and adjacent mud flat spanning the intertidal zone along the south coastline of the most heavily urbanized Deep bay, Guangdong province, China were analyzed. The average concentrations of mercury (Hg) in surface sediments of natural mangrove and restored mangrove were 172 and 151 ng g(-1), whereas those of copper (Cu) were 75 and 50 μg g(-1), respectively. Compared to those from other typical mangrove wetlands of the world, the metal levels in Shenzhen were at median to high levels, which is consistent with the fact that Shenzhen is in high exploitation and its mangrove suffer intensive impact from human activities. Hg and Cu concentration profiles indicated a higher metal accumulation in surface layers of sediments, in agreement with enrichment of organic matter contents. Maximum concentration, enrichment factors, and excess (background-deducted) concentration inventories of metals (Hg and Cu) were substantially different between environments, decreasing from natural mangrove sediments to restored mangrove sediments to mud flat. Furthermore, metal inputs to Futian mangrove decreased in the order natural mangrove > restored mangrove > mud flat, indicating that mangrove facilitated the accumulation and storage of Hg and Cu in sediment layers.

Characterizing the parent and oxygenated polycyclic aromatic hydrocarbons in mangrove sediments of Hong Kong

Parent and oxygenated polycyclic aromatic hydrocarbons (PAHs) were investigated in mangrove sediments of Hong Kong. Most of the analytes were detected, and the dominant carbonylic and hydroxylated PAHs in mangrove sediments were 9-fluorenone and 2-hydroxy fluorene, respectively. The concentration of 9-fluorenone and 9,10-anthraquinone was higher than their parent PAHs. Moreover, the concentration of total organic matter (TOM) related with those of the parent PAHs and carbonylic PAHs, except for hydroxylated PAHs, which indicated that TOM was not the only factor regulating the distribution of oxygenated PAHs. Nevertheless, the parent PAHs in mangrove sediments was correlated positively with carbonylic PAHs which demostrated not only the similar source but also the fate of these two compound class. However, hydroxylated PAHs had different source by comparing with parent PAHs and carbonylic PAHs, they were probably originated from biodegradation and accumulated in mangrove sediments.

Heavy metal and organic contaminants in mangrove ecosystems of China: a review

China's rapid economic growth has been accompanied by increasing environmental pollution. Mangrove ecosystems are now facing greater pollution pressures due to elevated chemical discharges from various land-based sources. Data on the levels of heavy metals and organic pollutants in mangrove compartments (sediments, plants, zoobenthos, and fish) in China over the past 20 years have been summarized to evaluate the current pollution status of the mangrove ecosystem. Overall, the Pearl River and Jiulong River estuaries were severely polluted spots. Concentrations of Cu, Zn, Cd, and Pb in mangrove sediments of Guangdong, Fujian, and Hong Kong were higher than those from Guangxi and Hainan. The pollution status was closely linked to industrialization and urbanization. The highest concentrations of polycyclic aromatic hydrocarbons (PAHs) were found in mangrove sediments from Hong Kong, followed by Fujian and Guangdong. Mangrove plants tend to have low-enriched ability for heavy metals and organic pollutants. Much higher levels of Pb, Cd, and Hg were observed in mollusks.

Effects of salinity on anatomical features and physiology of a semi-mangrove plant Myoporum bontioides

The effect of different concentrations of NaCl, 0, 100, 200, 300 and 400 mM, on the anatomical features and physiology of Myoporum bontioides was investigated. The photosynthetic rates (Pn) were significantly reduced by salt stress, with the lowest values at 400 mM NaCl. The content of malondialdehyde (MDA), proline and soluble sugar, as well as the activities of peroxidase (POD) and catalase (CAT) increased at the beginning, but became similar to the control as the experiment proceeded. The NaCl effect on superoxide dismutase (SOD) was different from the other parameters, with a significant reduction at 400 mM NaCl at Day 7. Salt glands were found in both upper and lower epidermis, and the ratios of the thickness of palisade to spongy mesophyll tissues increased with NaCl concentrations. The medullary ray was clearly damaged by NaCl at levels of 200 and 300 mM. These results demonstrated that M. bontioides could adapt to a relatively low salinity, and was not a halophilous species.

Effect of a polybrominated diphenyl ether congener (BDE-47) on growth and antioxidative enzymes of two mangrove plant species, Kandelia obovata and Avicennia marina, in South China

The effects of BDE-47 on the growth and antioxidative responses of the seedlings of Kandelia obovata (Ko) and Avicennia marina (Am) were compared in an 8-week hydroponic culture spiked with different levels of BDE-47, 0.1, 1, 5 and 10 mg l(-1). The two highest BDE-47 levels significantly suppressed the growth and increased the activities of three antioxidative enzymes, superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), of Ko in week 1. However, SOD and POD activities at high levels of BDE-47 became lower than the control in week 8. On the contrary, growth of Am was not affected at all contamination levels, and the activities of three enzymes were enhanced by BDE-47 in weeks 1 and 4, but such stimulatory effect became insignificant in week 8. Avicennia was more tolerant to BDE-47 toxicity than Kandelia, as its antioxidative enzymes could better counter-balance the oxidative stress caused by BDE-47.

Distribution and accumulation of polybrominated diphenyl ethers (PBDEs) in Hong Kong mangrove sediments

Polybrominated diphenyl ethers (PBDEs) have been used extensively as brominated flame retardants in various polymers, and have become serious environmental contaminants, particularly in coastal sediments. Mangrove wetlands are important coastal ecosystems in tropical and subtropical regions, and mangrove sediments are often the pollutant sinks due to their close proximity with human activities. In Hong Kong, sediment samples collected from five mangrove swamps were found to be contaminated with PBDEs and the eight measured BDE congeners, including BDE-28, -47, -99, -100, -153, -154, -183 and -209 were detected in all mangrove sediments, indicating that these pollutants were widespread in Hong Kong mangrove wetlands. Among the five swamps, relatively high concentrations of PBDEs were recorded in Mai Po mangrove swamp in the northwestern Hong Kong, which is part of the RAMSAR site but is severely influenced by the pollution from the Pearl River Delta. The depth profile of PBDEs in sediment cores collected from Mai Po also showed the inputs of PBDEs in this mangrove swamp increased year by year. In all sediments, the concentrations of BDE-209 were 1-2 orders of magnitude higher than the other congeners in the same sediment. The concentrations of BDE-209 and ∑PBDEs (defined as the sum of seven targeted BDE congeners except BDE-209) ranged from 1.53 to 75.9 ng g(-1) and from 0.57 to 14.4 ng g(-1), respectively. Among the targeted BDE congeners except BDE-209, slightly different composition was recorded among samples collected from different locations, with BDE-153 and -183 being the pre-dominated congeners. In all mangrove swamps, except Tai O in the southwest of Hong Kong, ∑PBDEs concentrations showed a common trend of landward>seaward>mudflat. The concentrations of ∑PBDEs were significantly correlated with total organic matter (TOM) content in sediments but not with the sediment particle sizes in each mangrove swamp.

Remobilization of polychlorinated biphenyls from sediment and its consequences for their transport in river waters

A laboratory experiment was performed to examine the remobilization of indicator polychlorinated biphenyls (iPCBs) from sediments and its results were applied to the real-world data for explaining the transport of PCBs in river. Seven PCB concentrations were determined in three series of model water-sediment systems (3 g of river sediment, three different volumes of distilled water (0.5, 0.25, and 0.15 ml), and 5 mg of biocide) after 11 days of incubation. Solid-phase extraction was used for separation of analytes from the aqueous phase and solvent extraction for isolation of analytes from the sediments, respectively. The extracts were analyzed for individual iPCB congeners using gas chromatography-mass spectrometry method. For each series of the experiment, the concentrations of PCBs in aqueous phase were similar. The average sediment/water partition coefficient value was 10(4) l/kg. The solubility of individual PCB congeners in water did not influence the desorption of PCBs from the sediment. Although the dominant form of PCBs in a water-sediment system occurs as suspended and colloidal fractions, these compounds are transported mostly in a dissolved form. Suspended and colloidal matter is a major sink for PCBs in low-energy aquatic environments. In contrast, the dissolved PCBs are readily transported in running waters. The mobilization of PCBs from sediments to aqueous phase, with respect to their solubility in water, seems to be limited, thus reducing the risk of secondary pollution.

Occurrence, bioavailability and toxic effects of trace metals and organic contaminants in mangrove ecosystems: a review

Although their ecological and socioeconomic importance has received recent attention, mangrove ecosystems are one of the most threatened tropical environments. Besides direct clearance, hydrological alterations, climatic changes or insect infestations, chemical pollution could be a significant contributor of mangrove degradation. The present paper reviews the current knowledge on the occurrence, bioavailability and toxic effects of trace contaminants in mangrove ecosystems. The literature confirmed that trace metals, Polycyclic Aromatic Hydrocarbons (PAHs), Persistent Organic Pollutants (POPs), Pharmaceuticals and Personal Care Products (PPCPs) and Endocrine Disrupters Compounds (EDCs) have been detected in various mangrove compartments (water, sediments and biota). In some cases, these chemicals have associated toxic effects on mangrove ecosystem species, with potential impact on populations and biodiversity in the field. However, nearly all studies about the bioavailability and toxic effects of contaminants in mangrove ecosystems focus on selected trace metals, PAHs or some "conventional" POPs, and virtually no data exist for other contaminant groups. The specificities of mangrove ecosystems (e.g. biology, physico-chemistry and hydrology) support the need for specific ecotoxicological tools. This review highlights the major data and methodological gaps which should be addressed to refine the risk assessment of trace pollutants in mangrove ecosystems.

The effect of mangrove reforestation on the accumulation of PCBs in sediment from different habitats in Guangdong, China

To investigate the influence of mangrove reforestation on the accumulation of PCBs, the concentrations and homologue patterns of polychlorinated biphenyls in surface sediments from different mangrove forests and their adjacent mud flats in Guangdong Province were determined. The total PCB concentrations in the sediments ranged from 3.03 to 46.62 ng g⁻¹ (dry weight). Differences in the accumulation and distribution of PCBs were found between the mangrove sites and the mud flats. Furthermore, the natural forests and restored mangrove forests of native species showed slight PCB contamination, whereas the exotic species Sonneratia apetala exacerbated the PCB pollution at certain sites. It was suggested that the native mangrove species Kandelia candel and Aegiceras corniculatum could represent good choices for the phytoremediation of PCB contamination.

Concentrations, spatial distributions and congener profiles of polychlorinated biphenyls in soils from a coastal city--Tianjin, China

A total of 82 surface soil samples collected from central urban sites, surrounding rural sites, coastal sites and background sites in Tianjin were analyzed for 84 PCB congeners. The mean values of total PCBs concentrations for surrounding rural sites, central urban sites, coastal sites, background sites and the whole Tianjin region were 4.45, 3.20, 12.65, 1.96 and 4.02 ng g(-1), respectively. No "urban fractionation effect" was found in Tianjin, which reflected the influence of local emission sources for PCBs such as industries and township enterprises in surrounding rural sites. In contrast, a "primary fractionation effect" was found in Tianjin region. The PCBs concentrations for whole Tianjin region showed a strong east-west gradient and the percentages of lighter molecular weight PCBs homologs (sum of di- to tetra-PCBs) to the total PCBs concentrations increased from east to west. The seven indicator PCBs concentrations were well correlated with the total PCBs concentrations with the correlation coefficients as 0.76 for Tianjin region and 0.74 for central urban sites, respectively. Predominant PCB homolog groups were penta- and tri-PCBs for Tianjin region. 10 dioxin-like PCBs concentrations were well correlated with total PCBs concentrations for all the sampling sites (R=0.79, P<0.0001). The TEQ concentrations for 10 dioxin-like PCBs were 5.3424 ng kg(-1) for Tianjin region and showed a strong east to west gradient. The spatial distribution of PCBs levels, homolog composition patterns and TEQ concentrations were all obviously influenced by local emission sources for PCBs in the east part of Tianjin region.

Superficial distribution of aromatic compounds and geomicrobiology of sediments from Suruí Mangrove, Guanabara Bay, RJ, Brazil

The distribution of selected aromatic compounds and microbiology were assessed in superficial sediments from Suruí Mangrove, Guanabara Bay. Samples were collected at 23 stations, and particle size, organic matter, aromatic compounds, microbiology activity, biopolymers, and topography were determined. The concentration of aromatic compounds was distributed in patches over the entire mangrove, and their highest total concentration was determinated in the mangrove's central area. Particle size differed from most mangroves in that Suruí Mangrove has chernies on the edges and in front of the mangrove, and sand across the whole surface, which hampers the relationship between particle size and hydrocarbons. An average @ 10% p/p of organic matter was obtained, and biopolymers presented high concentrations, especially in the central and back areas of the mangrove. The biopolymers were distributed in high concentrations. The presence of fine sediments is an important factor in hydrocarbon accumulation. With high concentration of organic matter and biopolymers, and the topography with chernies and roots protecting the mangrove, calmer areas are created with the deposition of material transported by wave action. Compared to global distributions, concentrations of aromatic compounds in Suruí Mangrove may be classified from moderate to high, showing that the studied area is highly impacted.

Modulation of steroidogenesis by coastal waters and sewage effluents of Hong Kong, China, using the H295R assay

BACKGROUND, AIM, AND SCOPE

The presence of a variety of pollutants in the aquatic environment that can potentially interfere with the production of sex steroid hormones in wildlife and humans has been of increasing concern. The aim of the present study was to investigate the effects of extracts from Hong Kong marine waters, and influents and effluents from wastewater treatment plants on steroidogenesis using the H295R cell bioassay. After exposing H295R cells to extracts of water, the expression of four steroidogenic genes and the production of three steroid hormones were measured.

MATERIALS AND METHODS

Water samples were collected during the summer of 2005 from 24 coastal marine areas and from the influents and effluents of two major waste water treatment plants (WWTPs) in Hong Kong, China. Samples were extracted by solid phase extraction (SPE). H295R cells were exposed for 48 h to dilutions of these extracts. Modulations of the expression of the steroidogenic genes CYP19, CYP17, 3betaHSD2, and CYP11beta2 were determined by measuring mRNA concentrations by real-time polymerase chain reaction (Q-RT-PCR). Production of the hormones progesterone (P), estradiol (E2), and testosterone (T) was quantified using enzyme linked immunosorbent assays (ELISA).

RESULTS

Extracts from samples collected in two fish culture areas inhibited growth and proliferation of H295R cells at concentrations greater or equal to 10(5) L equivalents. The cells were exposed to the equivalent concentration of active substances in 10,000 L of water. Thus, to observe the same level of effect as observed in vitro on aquatic organisms would require a bioaccumulation factor of this same magnitude. None of the other 22 marine samples affected growth of the cells at any dilution tested. Twelve of the marine water samples completely inhibited the expression of CYP19 without affecting E2 production; inhibition of CYP17 expression was observed only in one of the samples while expression of CYP11beta2 was induced as much as five- and ninefold after exposure of cells to extracts from two locations. The expression of the progesterone gene 3betaHSD2 was not affected by any of the samples; only one sample induced approximately fourfold the production of E2. Although more than twofold inductions were observed for P and T production, none of these values were statistically significant to conclude effects on the production of these two hormones. While influents from WWTPs did not affect gene expression, an approximately 30% inhibition in the production of E2 and a 40% increase in P occurred for the exposure with influents from the Sha Tin and Stonecutters WWTPs, respectively. Effluents from WWTPs did not affect the production of any of the studied hormones, but a decrement in the expression of the aldosterone gene CYP11beta2 was observed for the Sha Tin WWTP exposure. No direct correlation could be established between gene expression and hormone production.

DISCUSSION

Observed cytotoxicity in the two samples from fish culture areas suggest the presence of toxic compounds; chemical analysis is required for their full identification. Although effluents from WWTPs did not affect hormone production, other types of endocrine activity such as receptor-mediated effects cannot be ruled out. Interactions due to the complexity of the samples and alternative steroidogenic pathways might explain the lack of correlation between gene expression and hormone production results.

CONCLUSIONS

Changes observed in gene expression and hormone production suggest the presence in Hong Kong coastal waters of pollutants with endocrine disruption potential and others of significant toxic effects. The aromatase and aldosterone genes seem to be the most affected by the exposures, while E2 and P are the hormones with more significant changes observed. Results also suggest effectiveness in the removing of compounds with endocrine activity by the WWTPs studied, as effluent samples did not significantly affect hormone production. The H295R cell showed to be a valuable toll in the battery required for the analysis of endocrine disrupting activities of complex environmental samples.

RECOMMENDATIONS AND PERSPECTIVES

Due to the intrinsic complexity of environmental samples, a combination of analytical tools is required to realistically assess environmental conditions, especially in aquatic systems. In the evaluation of endocrine disrupting activities, the H295R cell bioassay should be used in combination with other genomic, biological, chemical, and hydrological tests to establish viable modes for endocrine disruption and identify compounds responsible for the observed effects.

Historical trends of organic pollutants in sediment cores from Hong Kong

Recent studies have indicated the occurrence of a wide range of trace organic contaminants, including polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) in the Hong Kong environment. These contaminants are potentially harmful to ecological systems, particularly in coastal areas. In this study, two sediment cores (4m) were collected from southern waters of Hong Kong in 2004 to study the historical trends, distribution patterns, and potential sources of trace organic contaminants. DDTs (p,p'-DDT, o,p'-DDT, p,p'-DDD, o,p'-DDD and p,p'-DDE), hexachlorohexanes (HCHs) (alpha and gamma), hexachlorobenzene (HCB), and PCBs were detected in the samples, whereas other target compounds were all below detection limits. Many OCPs have not been produced or used for many years due to toxicological or environmental concerns and PCB use is prohibited in Hong Kong. However, some compounds were still detectable in recent years, and were found to be widely distributed in the environment, likely because of pollutant inputs from the highly industrialized Pearl River Delta region. These results provide important information on current and historical contamination in Hong Kong, and help to reconstruct the pollution history of these trace organic pollutants in Hong Kong coastal waters.

Distribution of persistent organochlorine residues in sediments from the Songhuajiang River, Northeast China

Organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in surface sediments from 10 sampling sites of the Songhuajiang River were analyzed to evaluate their potential pollution and hazards. Gas chromatography equipped with a 63Ni electron capture detector (GC-ECD) and gas chromatography/mass spectrometer (GC/MS) methods were used, respectively. The total concentrations of 13 OCPs varied from 4.26 to 18.45 ng g(-1). Sigma HCH (alpha-HCH, beta-HCH, delta-HCH, gamma-HCH), sigma DDT (p, p'-DDE, p, p'-DDD, o,p'-DDT, p, p'-DDT) and sigma Cyclodiene (Heptachlor, Aldrin, Heptachlor epoxide, Dieldrin, Endrin) ranged from 2.42 to 7.95, 0.14 to 5.12, 0.55 to 6.01 ng g(-1), respectively. The most dominant pollutant among the OCPs was gamma-HCH with the concentration of 3.4 (0.77 to 7.21) ng g(-1). Total PCB concentrations ranged between 0.59 and 15.93 ng g(-1). Low chlorinated biphenyls (tri- and tetra-) dominated in total PCBs. Positive correlations were observed between the EDDT, sigma Cyclodiene, sigma OCP or sigma PCB and TOC of the sediments (P < 0.05, n = 10). No obvious correlation was observed between the sigma HCH and the TOC of the sediments.

Monitoring and assessment of persistent organochlorine residues in sediments from the Daliaohe River watershed, northeast of China

Surface sediment samples from 12 sites of the three selected rivers in Daliaohe River watershed (Hunhe River, Taizihe River and Daliaohe River) were analyzed with the objective of establishing sources and hazard of the organochlorinae pesticides (OCPs) and polychlorinated biphenyl (PCBs) in surface sediments. The total concentrations of OCPs varied from 3.06 to 23.24 ng g(-1). SigmaHCH (alpha-HCH, beta-HCH, delta-HCH, gamma-HCH), SigmaDDT (p, p'-DDE, p, p'-DDD, o, p'-DDT, p, p'-DDT) and SigmaCyclodiene (Heptachlor, Aldrin, Heptachlor epoxide, Dieldrin, Endrin) ranged from 1.86 to 21.48, 0.5 to 2.81 and 0.56 to 1.53 ng g(-1), respectively. Results of OCPs also illustrate that the most dominant pollutants among the OCPs was SigmaHCH, and gamma-HCH was the most dominant isomer in HCH, which was evidence of recent input of lindane. It possibly came from the runoff of polluted soils and long-scale transportation. Total PCB concentrations ranged between 1.88 and 16.88 ng g(-1). The peak concentrations of PCBs were found in sediments from station T5 and D3, which are in the vicinity of industrial areas and ferry, respectively. These data show a moderate level of OCPs and PCBs contaminations compared to that in other countries.

Distribution patterns of nitrobenzenes and polychlorinated biphenyls in water, suspended particulate matter and sediment from mid- and down-stream of the Yellow River (China)

Samples of water, suspended particulate matter (SPM) and sediment were collected from mid- and down-stream of the Yellow River. The distribution and concentration of 10 nitroaromatic compounds and polychlorinated biphenyls (PCBs) were extensively studied. The total concentration of 10 nitrobenzenes (SigmaNBs) varied from 0.269 to 9.052 microg l(-1) in water, from 2.916 to 164.4 microg kg(-1) dry weight in SPM, and from 0.954 to 14.72 microg kg(-1) dry weight in sediment. PCBs associated with the sediments, measured as the summed responses of Aroclor 1242, 1248, 1254, 1260 (in comparison to those of a standard 1:1:1:1 mixture), were found to be in the range of non-detectable to 5.98 microg kg(-1). In the samples collected, various PCB congeners showed similar distribution characteristics with congeners containing 3-5 chlorine atoms accounting for more than 96.4% of total PCB. In most of the samples, PCB concentrations occurred in the order: TetraCB > TriCB > PentaCB. Levels of SigmaNBs in the Yellow River were relatively low in comparison with values reported from other river and marine systems, and PCB levels were comparatively low. Relative to the PCBs, SigmaNBs showed significantly more difference among the various stations, presumably due to the influence of different pollution sources. No obvious correlation was observed between the pollutant concentrations and either the TOC or the grain size of the sediments.

Vertical fluxes and accumulation of PCBs in coastal sediments of the Río de la Plata estuary, Argentina

Settling particles and underlying sediments collected at 1, 2.5 and 4 km along offshore transects in the urbanized sector of the Río de la Plata were analyzed to evaluate the sources and accumulation of PCBs. Total PCB concentrations range from <0.1 to 100 ng g(-1) and include variability associated to North-South and offshore gradients reflecting the impact of coastal discharges. Highest concentrations were recorded in the industrialized Central area close to Buenos Aires (61+/-37 ng g(-1) at 1 km) relative to cleaner northern stations (3.6+/-2.2 ng g(-1)) and southward sites (37+/-2.8 ng g(-1)), affected by transport of particulate PCBs by coastal currents. Sediment traps deployed in the Central area revealed large depositional fluxes of total matter (361+/-124 gm(-2)day(-1)) and PCBs (26+/-19 microg m(-2)day(-1)) and high sedimentation rates (5.0+/-1.7 cm yr(-1)). Uniform PCB concentrations (66-89 ng g(-1)) down to 20 cm in sediment cores suggest continued PCB discharges during the last 4 years. PCB composition was dominated by hexa (43+/-6.4%), hepta (23+/-5.1%) and pentachlorobiphenyls (21+/-5.5%) with lower proportions tri-tetra (7.4+/-5.4%) and higher chlorinated congeners (5.1+/-3.3%). A consistent weathering pattern with loss of 3-5 chlorobiphenyls and enrichment in higher chlorinated PCBs corresponding to a shift from a 1:1 to a 1:3 1254:1260 Aroclor mixture, was observed offshore. A principal component analysis performed with the relative contribution of PCB congener classes confirmed the offshore weathering pattern indicating that transformer oils containing Aroclor 1254-1260 are the most probable sources. Sediment inventories, sediment trap fluxes and Fugacity II calculations indicate an accumulation approximately 500-800 kg PCB in superficial sediments of this coastal environment.

Persistent organic pollutants in mangrove food webs in Singapore

In this study, persistent organic pollutants were quantified in sediments, subsurface seawater, sea-surface microlayer and twenty-four biota species collected at two separate mangrove habitats in Singapore. Data confirmed the ubiquity of POPs, including polybrominated diphenyl ethers (PBDEs), in the marine environment of Singapore. A biomagnification phenomenon was observed amongst the species collected and analysed from both mangrove sites studied. Thunder crabs and fish displayed the highest POP levels. Congener profiles of PBDEs varied amongst mangrove biota species and suggested different metabolic pathways exist for flame retardants. Similarly, crab species showed an ability to metabolize chlordane insecticide.

Polychlorinated biphenyls and organochlorine pesticides in human adipose tissue and breast milk collected in Hong Kong

Contamination from persistent organic pollutants is a pervasive global problem that urgently demands global concern and action. In the present study, concentrations of organochlorine (OC) pesticides and polychlorinated biphenyls (PCBs) were determined in 37 samples of female adipose tissue collected in Hong Kong hospitals. Among the pollutants analyzed, DDTs (2.79 ng/g fat), HCHs (0.72 ng/g fat), and PCBs (0.19 ng/g fat) were prominent compounds in most of the adipose tissue. p,p'-DDE and hexachlorinated biphenyls were found in all samples, whereas heptachlor epoxide and dieldrin were found only in some samples. An estimation of toxic equivalency concentration (TEQ) due to dioxin-like coplanar PCBs was also performed. The estimated TEQ(PCBs) was 2.01 pg/g fat. This study also compared our previous results obtained from the milk samples of the same donors. Significant correlations are obtained for DDTs and HCHs between milk and adipose tissue. Detailed review of available information concerning OC pesticides and PCBs in different ecological compartments indicated that bioconcentration and biomagnification of these contaminants are common phenomena of the Pearl River Delta region, which has undergone rapid socioeconomic change in the past 20 years. It is suggested to establish a regional organization in order to coordinate the monitoring of persistent organic pollutants in the region.

Genotoxicity of field-collected inter-tidal sediments from Cork Harbor, Ireland, to juvenile turbot (Scophthalmus maximus L.) as measured by the Comet assay

The alkaline single cell gel electrophoresis (SCGE) or Comet assay was employed to test the potential of surficial sediment collected from Cork Harbor, Ireland, to induce DNA damage in turbot (Scophthalmus maximus L.) in a laboratory exposure experiment. Turbot were exposed for 21 days to field-collected sediment from Cork Harbor and from a relatively clean reference site at Ballymacoda and sampled at 0, 7, 14, and 21 days. As a positive control for the sediment exposure experiment, a subsample of the turbot was exposed to cadmium chloride-spiked seawater. DNA damage analysis was performed on epidermal, gill, spleen, liver, and whole blood cell preparations. Liver, gill, and blood were the most sensitive tissues while a lower level of damage was detected in the epidermis and spleen. The blood was determined to be a suitable predictor of DNA damage in the whole organism. Chemical analysis of the sediment indicated that polycyclic aromatic hydrocarbons formed the bulk of the contaminants, with the harbor sites having almost double the levels of those from the reference site. The data indicated that turbot exposed to sediments from Cork Harbor elicited a significant increase in DNA damage in comparison with those exposed to sediment from the reference site and that exposure to the contaminated sediments caused a multi-organ genotoxic response. Results from the study indicate a relationship between the presence of genotoxicants in sediment and DNA damage. This finding was encouraging with regard to the potential use of the Comet assay as part of a marine biomonitoring strategy.

Harmonisation of polychlorinated biphenyl (PCB) analyses for ecotoxicological interpretations of southeast Asian environmental media: what's the problem?

Within the southeast Asian region, an issue has arisen about how polychlorinated biphenyls (PCBs) should be analysed in environmental samples for risk assessment purposes. Should PCBs be identified as Aroclors (or other commercial mixtures such as Kanechlors), as homologues, as PCB congeners, or as toxic equivalents? The debate appears to centre around separate disciplines that are involved in environmental measurement and analyses, specifically the reporting needs of the environmental chemists and toxicologists. The choice of PCB measurements is generally made on the basis of what question is being asked. This viewpoint presents a general description of the issue, identifies the differences amongst measurement techniques (significance of analytical results, the application and reliability of data, and general costs), characterises the current status of PCB analyses and reporting in the southeast Asian region (specifically, in Cambodia, China, Hong Kong, India, Indonesia, Korea, Japan, the Philippines, Thailand and Vietnam), and proposes a recommended approach for harmonising analytical and toxicological results from laboratories and research groups who are interested in investigating the fate and effects of PCBs on marine/estuarine biota in the region.

Horizontal and vertical distribution of PCBs and chlorinated pesticides in sediments from Masan Bay, Korea

Horizontal and vertical distributions of organochlorine compounds (OCs) were determined in sediments from Masan Bay. The concentrations of polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethanes (DDTs), HCB, hexachlorocyclohexanes (HCHs) and chlordane related compounds (CHLs) in sediments were in the range of 1.24-41.4, 0.28-89.2, 0.02-0.59, nd-1.03, and nd-2.56 ng/g, respectively. The spatial distribution of OCs showed a negative gradient from the inner of the bay to outer part of the bay, indicating that the source of OCs was probably located inside the bay. Compositional pattern of PCB congeners showed a relatively high concentration of high-chlorinated congeners in the inner part of the bay and a relatively low concentration of low-chlorinated congeners in the outer part. In sediment core from Masan Bay maximum concentrations of PCBs and DDTs are observed in the subsurface samples and correspond to an age of early 1980s and late 1960s. The concentration profiles of PCBs and DDTs in sediments of Masan Bay appear to correspond to use of PCBs and DDTs in Korea.