Plant performance, dioxygenase-expressing rhizosphere bacteria, and biodegradation of weathered hydrocarbons in contaminated soil

Two greenhouse pot experiments were conducted to investigate the potential of 13 plant species (grasses, cruciferes, legumes, herbs) to thrive in a long-term contaminated soil from a former manufactured gas plant (MGP) site, to promote the proliferation of total and aromatic ring dioxygenase-expressing bacteria (ARDB) in the root zone, and to foster the biodegradation of petrol hydrocarbons (PHCs) and polycyclic aromatic hydrocarbons (PAHs). PHCs at 23200 mg kg(-1) and PAHs at 2194 mg kg(-1) reduced seed germination, plant survival, and shoot yields for most plants. Total bacteria and ARDB were generally more abundant in contaminated soil and were most numerous in the rhizosphere of mustard. During 68 d, the loss of total petrol hydrocarbons (TPHs) and total US EPA priority PAHs (TPAHs) was greatest in soil planted with hemp and mustard. Pea, cress, and pansy increased the amounts of PAHs extracted from soil, including an almost 60% increase for dibenzo(ah)anthracene. Plants may enhance the chemical extractability and perhaps biological availability of initially unextractable molecules.     

Distributions and concentrations of PAHs in Hong Kong soils

Surface soil (0-10 cm) samples from 53 sampling sites including rural and urban areas of Hong Kong were collected and analyzed for 16 EPA priority polycyclic aromatic hydrocarbons (PAHs). Total PAH concentrations were in the range of 7.0-410 microg kg(-1) (dry wt), with higher concentrations in urban soils than that in rural soils. The three predominant PAHs were Fluoranthene, Naphthalene and Pyrene in rural soils, while Fluoranthene, Naphthalene and Benzo(b + k)fluoranthene dominated the PAHs of urban soils. The values of PAHs isomer indicated that biomass burning might be the major origin of PAHs in rural soils, but vehicular emission around the heavy traffic roads might contribute to the soil PAHs in urban areas. A cluster analysis was performed and grouped the detectable PAHs under 4 clusters, which could be indicative of the PAHs with different origins and PAHs affected by soil organic carbon contents respectively.     

DDT levels in human milk in Hong Kong, 2001-02

High levels of p,p'-DDT were detected in Hong Kong breast milk sampled in 1976 and 1985. Monitoring DDT levels in human breast milk in this region is important to identify trends in exposure. As part of the 2002-03 WHO/EURO coordinated exposure study, the concentrations of DDT and its metabolites were determined in 10 pooled milk samples classified by geographic origin and dietary history, comprising milk samples from 238 primiparous mothers giving birth in Hong Kong. Analysis was performed by Gas Chromatography (GC) with electron capture detector and confirmed by GC/Mass Spectrometry. The sum-DDT concentration (range: 0.92-2.05mg/kg fat) was age-dependent and indicated a decreasing trend since the 1970s. Mothers who recently came from mainland China had higher p,p'-DDT to p,p'-DDE ratios, suggesting a more recent exposure compared to women mainly residing in Hong Kong. The average Hong Kong sum-DDT level (1.50mg/kg fat) was among the highest of the contemporary levels (range: 0.12-1.97mg/kg fat; median: 0.40mg/kg fat) in the 16 countries/regions participating in the 2002-03 WHO/EURO exposure study. This is probably due to the previous extensive DDT exposure and continuing use of DDT in agriculture in mainland China. Despite the apparent decrease of DDT body load over 30 years, the environmental health hazard from DDT contamination in the Pearl River Delta region remains a concern. Measures to eradicate illegal use of DDT in mainland China and regular food monitoring programs are needed in the region. Despite the presence of DDT and other persistent organic pollutants in human breast milk, breastfeeding should continue to be strongly supported for its life-long benefits to infants.     

Occurrence of organic contaminants in sewage sludges from eleven wastewater treatment plants, China

This study presents the occurrence of 43 semi-volatile organic compounds (SVOCs) listed as priority pollutants by both China and the United States Environmental Protection Agency, in sewage sludges collected from eleven wastewater treatment plants (WWTPs) of mainland and Hong Kong, China. Thirty-six SVOCs were detected by gas chromatography coupled with mass spectrometer (GC-MS) and at least 14 in each sample. The most abundant compounds were phthalic acid esters (PAEs) and polycyclic aromatic hydrocarbons (PAHs) with total concentrations ranging from 10 to 114mgkg(-1) dry weight (d.w.) (with a mean of 30mgkg(-1) d.w.) and from 1.4 to 33mgkg(-1)d.w. (with a mean of 16mgkg(-1) d.w.), respectively, followed by chlorobenzenes, nitroaromatics, haloethers and halogenated hydrocarbons which occurred generally at concentrations lower than 10mgkg(-1) d.w. Large variations were observed between the concentrations of individual compounds as well as their total concentrations in sludge samples from different WWTPs. The highest values of sum concentration of 16 PAHs and of 6 PAEs were found in sewage sludge from Beijing. The mean total concentration of each class of SVOCs in sewage sludge from mainland was remarkably higher than that from Hong Kong. The concentrations of di(2-ethylhexyl) phthalate in 91% sludge samples met the limit (100mgkg(-1)d.w.) proposed by the Europe Union for land application, whereas the PAH concentrations of 64% sludge samples exceeded the maximum permissible concentration (6.0mgkg(-1)d.w.). The occurrence of SVOCs in this study are compared with other studies and their sources are discussed.     

Polycyclic aromatic hydrocarbons (PAHs) and carbonyl compounds in urban atmosphere of Hong Kong

Polycyclic aromatic hydrocarbons (PAHs) and carbonyls compounds are becoming a major component of atmospheric toxic air pollutants (TAPs) in Hong Kong. Many studies in Hong Kong show that traffic emission is one of the most significant contributors in urban area of Hong Kong. A twelve months monitoring program for PAHs and carbonyl compounds started on 10 April 1999 including a two weeks intensive sampling in winter had been performed at a roadside urban station at Hong Kong Polytechnic University in order to determine the monthly and seasonal variations of PAHs and carbonyl concentrations. The objective of this study is to characterize the roadside concentrations of selected TAPs (PAHs and carbonyl compounds) and to compare with the long-term compliance monitoring data acquired by Hong Kong Environmental Protection Department (EPD). Monthly variations, seasonal variations and winter/summer ratios at the monitoring station are discussed.     

Chemical and microbiological qualities of The East River (Dongjiang) water,with particular reference to drinking water supply in Hong Kong

Currently, about 80% of drinking water in Hong Kong is abstracted from The East River (Dongjiang) that is located in the mainland side of China. Literature records and monitoring results of 2000-2001 confirmed that the lower section of the Dongjiang had been contaminated by organic and inorganic pollutants. Statistical analyses showed that the increases of total cadmium, copper and zinc in the surface layer of sediment of Hong Kong reservoirs from 1994 to 2001 were positively correlated (significant at p<0.05) with those in the surface layer of sediments of the lower Dongjiang. Recent microbiological survey revealed that pathogens such as Salmonella spp., Vibro spp., Giardia lamblia and Cryptosporidium parvum appeared occasionally in water samples of the Dongjiang and Hong Kong reservoirs. While analytical results found that currently most of the heavy metals, trace organics and microbes were removed by the drinking water treatment plants in Hong Kong, the long-term health risk of drinking water contamination should not be overlooked. The Water Supplies Department of Hong Kong is recommended to intensify its water quality monitoring program to cover pathogenic bacteria and parasites in watercourses and reservoirs.     

Residues of organochlorine pesticides in Hong Kong soils

It was short of research on the organochlorine pesticides (OCPs) residues in the soils of Hong Kong. Sixty-six representative soil samples were collected from the 46 sites covering five types of land uses in Hong Kong. Hexachlorohexanes (HCH) and 7 Stockholm Convention OCPs were analyzed by gas chromatograph (GC) equipped with a Nickel 63 electronic capture detector (muECD). The results presented that HCH and 5 Stockholm Convention pesticides were detected in Hong Kong soils although the detectable ratio varies to a great extent. The concentration sequence of the five detectable OCPs was HCH > dichlorodiphenyltrichloroethane (DDT) > hexachlorobenzene (HCB) approximately = Endrin > alpha-endosulfan. Among the OCPs and their homologues or isomers, beta-HCH and p,p'-DDE were the two predominant substances according to the concentrations and detectable ratios, concentrations of which in soils were averagely 6.12 microg kg(-1) and 0.41 microg kg(-1) respectively. Soil horizon samples of 0-10 cm, 10-30 cm and >30 cm depth were selected from nine soil profiles to demonstrate the depth distributions of DDT and HCH in soil profiles. Concentrations of HCH tended to increase gradually from the topsoil to bottom layer while the lowest concentration of DDT is usually found in the subsoil (10-30 cm) in most sampling sites. In addition, close correlations of pH(KCl) and total organic carbon (TOC) with HCH indicated an effect on the residues of HCH caused by these two soils properties, but such relationships were not found with DDT or other OCPs.     

Contamination of butyltin and phenyltin compounds in the marine environment of Otsuchi Bay, Japan

Butyltin (BT) and phenyltin (PT) compounds were measured in seawater, sediment, and biological samples collected from coastal areas of Otsuchi Bay, Japan. Tributyltin (TBT) compounds in seawater, sediment, plankton, mussels, scallops and fish were in the range of 0.008-0.074 microg liter(-1), 0.01-0.64 mg (kg dry wt)(-1), 0.24-9.8 mg (kg dry wt)(-1), 0.04-0.18 mg (kg wet wt)(-1), 0.10-0.13 mg (kg wet wt)(-1) and 0.01-0.02 mg (kg wet wt)(-1), respectively. Trace amount of PTs were found in seawater. The highest concentrations of TBT and triphenyltin (TPT) were found near a shipyard. Triorganotin compounds were more dominant than their metabolites. A positive correlation was observed between the concentrations of TBT and TPT in the mussels. Concentrations of TBT and TPT in mussels were high in the upper intertidal zone, and decreased toward the water.     

Seasonal and spatial variation of solvent extractable organic compounds in fine suspended particulate matter in Hong Kong

The results of a 12-month study of more than 100 solvent extractable organic compounds (SEOC) in particulate matter (PM) less than or equal to 2.5 microm (PM2.5) collected at three air monitoring stations located at roadside, urban, and rural sites in Hong Kong are reported. The total yield of SEOC that accounts for approximately 8-18% of organic carbon (OC) determined by a thermal optical transmittance method was 125-2060 ng/m3, which included 14.6-128 ng/m3 resolved aliphatic hydrocarbons, 39.4-1380 ng/m3 unresolved complex mixtures, 0.6-17.2 ng/m3 polycyclic aromatic hydrocarbons, 41.6-520 ng/m3 fatty acids, and < 0.1-12.1 ng/m3 alkanols. Distinct seasonal variations (summer/winter differences) were observed with higher concentrations of the total and each class of SEOC in the winter and lower concentrations in the summer. Spatial variations are also obvious, with the roadside samples having the highest concentrations of SEOC and the rural samples having the lowest concentrations in all seasons. Characteristic ratios of petroleum hydrocarbons, such as carbon preference index, unresolved to resolved components, and carbon number with maximum concentration, suggest that PM2.5 carbon in Hong Kong originates from both biogenic and anthropogenic sources. The proportion of SEOC in PM2.5 from anthropogenic sources is estimated.     

Retention and distribution of heavy metals in mangrove soils receiving wastewater

The distribution and chemical fractionation of heavy metals retained in mangrove soils receiving wastewater were examined by soil column leaching experiments. The columns, filled with mangrove soils collected from two swamps in Hong Kong and the People's Republic of China, were irrigated three times a week for 150 days with synthetic wastewater containing 4 mg l(-1) Cu, 20 mg l(-1) Zn, 20 mg l(-1) Mn and 0.4 mg l(-1) Cd. Soil columns leached with artificial seawater (without any heavy metals) were used as the control. At the end of the leaching experiments, soil samples from each column were divided into five layers according to its depth viz. 0-1, 1-3, 3-5, 5-10 and > 10 cm, and analyzed for total and extractable heavy metal content. The fractionation of heavy metals in the surface soil samples (0-1 cm) was investigated by the sequential extraction technique. In both types of mangrove soils, the surface layer (0-1 cm) of the columns receiving wastewater had significantly higher concentrations of total Cu, Cd, Mn and Zn than the control. Concentrations declined significantly with soil depth. The proportion of exchangeable heavy metals in soils receiving wastewater was significantly higher than that found in the control, about 30% of the total heavy metals accumulated in the soil masses of the treated columns were extracted by ammonium acetate at pH 4. The sequential extraction results show that in native mangrove soils (the soils without any treatment), the major portion of Cu, Zn, Mn and Cd was associated with the residual and precipitated fractions with very low concentrations in more labile phases. However, in mangrove soils receiving wastewater, a significantly higher percentage of Mn, Zn and Cd was found in the water-soluble and exchangeable fractions. Copper appeared to be more strongly adsorbed in mangrove soils than the other heavy metals. In general, heavy metal accumulation in the surface mangrove soils collected in Hong Kong was higher than those in the PRC, although the metals in the latter soil type were more strongly bound. These findings suggest that whether the heavy metal retained in managrove soils becomes a secondary source or a permanent sink would depend on the kinds of heavy metals and also the types of mangrove soils.     

Sorption of native polyaromatic hydrocarbons (PAH) to black carbon and amended activated carbon in soil

Organic pollutants (e.g. polyaromatic hydrocarbons (PAH)) strongly sorb to carbonaceous sorbents such as black carbon and activated carbon (BC and AC, respectively). For a creosote-contaminated soil (Sigma15PAH 5500 mg kg(dry weight(dw))(-1)) and an urban soil with moderate PAH content (Sigma15PAH 38 mg kg(dw)(-1)), total organic carbon-water distribution coefficients (K(TOC)) were up to a factor of 100 above values for amorphous (humic) organic carbon obtained by a frequently used Linear-Free-Energy Relationship. This increase could be explained by inclusion of BC (urban soil) or oil (creosote-contaminated soil) into the sorption model. AC is a manufactured sorbent for organic pollutants with similar strong sorption properties as the combustion by-product BC. AC has the potential to be used for in situ remediation of contaminated soils and sediments. The addition of small amounts of powdered AC (2%) to the moderately contaminated urban soil reduced the freely dissolved aqueous concentration of native PAH in soil/water suspensions up to 99%. For granulated AC amended to the urban soil, the reduction in freely dissolved concentrations was not as strong (median 64%), especially for the heavier PAH. This is probably due to blockage of the pore system of granulated AC resulting in AC deactivation by soil components. For powdered and granulated AC amended to the heavily contaminated creosote soil, median reductions were 63% and 4%, respectively, probably due to saturation of AC sorption sites by the high PAH concentrations and/or blockage of sorption sites and pores by oil.     

Comparison of PM2.5 carbon measurement methods in Hong Kong, China

Samples from Hong Kong, China, were analyzed for organic carbon (OC), elemental carbon (EC), and total carbon (TC) by three thermal protocols (low-temperature IMPROVE and high-temperature STN and NIOSH) and two optical monitoring methods: reflectance and transmittance. Good agreement (+/-10%) for TC among the three protocols was observed for sample loadings of 1-55 microg m(-3). The two protocols using a reflectance pyrolysis correction showed best agreement for EC, with <20% differences found for approximately 80% of the samples. Hong Kong has a large diesel fleet, and for some heavily loaded samples the light transmittance was too low for quantitative detection, resulting in large uncertainties in the OC/EC split based on transmittance. Hong Kong experienced OC levels similar to those at US sites, but has much higher EC concentrations. OC/EC ratios range from 2 to 5 at two US sites and from 0.2 to 1.2 at three Hong Kong sites.     

Polychlorinated biphenyls (PCBs) in sediments in Hong Kong: a congener-specific approach to the study of coplanar PCBs in aquatic ecosystems

Patterns of contamination by polychlorinated biphenyls (PCBs) were investigated in fourteen samples of coastal sediments from Hong Kong. Congener-specific analyses revealed nine sediment samples from Junk Bay to contain PCBs at concentrations ranging from 31 to 2200 ng g(-1) dry weight, concentrations generally increasing with distance north in the Bay. By contrast, five sediments from the Tolo area to the north-east of Hong Kong exhibited total PCB levels of only 6.6 to 45 ng g(-) dry weight. The patterns of relative abundance of PCB congeners in the northern Junk Bay sediments suggested the existence of ongoing source(s) of PCBs in this area; biphenyls of lower chlorination were present at high concentration in these samples. Three coplanar PCBs (3', 4, 4'-tetrachlorobiphenyl; 3,3',4,4',5-pentachlorobiphenyl; and 3,3',4,4',5,5'-hexachlorobiphenyl) were found to be present in Junk Bay sediments; these are highly toxic and are cause for concern in aquatic environments. The abundance of the three coplanar PCBs in the sediments studied was similar to that in commercial PCB mixtures, suggesting that these congeners are not enriched over other PCBs by the sediments of coastal ecosystems. It is concluded that the preferential enrichment of coplanar PCBs occurs in the biosphere, rather than in sediments.     

Symbiotic efficiency of autochthonous arbuscular mycorrhizal fungus (G. mosseae) and Brevibacillus sp. isolated from cadmium polluted soil under increasing cadmium levels

The effect of inoculation with indigenous naturally occurring microorganisms (an arbuscular mycorrhizal (AM) fungus and rhizosphere bacteria) isolated from a Cd polluted soil was assayed on Trifolium repens growing in soil contaminated with a range of Cd. One of the bacterial isolate showed a marked PGPR effect and was identified as a Brevibacillus sp. Mycorrhizal colonization also enhanced Trifolium growth and N, P, Zn and Ni content and the dually inoculated (AM fungus plus Brevibacillus sp.) plants achieved further growth and nutrition and less Cd concentration, particularly at the highest Cd level. Increasing Cd level in the soil decreased Zn and Pb shoot accumulation. Coinoculation of Brevibacillus sp. and AM fungus increased shoot biomass over single mycorrhizal plants by 18% (at 13.6 mg Cd kg(-1)), 26% (at 33.0 mg Cd kg(-1)) and 35% (at 85.1 mg Cd (kg(1)). In contrast, Cd transfer from soil to plants was substantially reduced and at the highest Cd level Brevibacillus sp. lowered this value by 37.5% in AM plants. Increasing Cd level highly reduced plant mycorrhization and nodulation. Strong positive effect of the bacterium on inocula, are important in plant Cd tolerance and development in Cd polluted soils.     

Ectomycorrhizas impede phytoremediation of polycyclic aromatic hydrocarbons (PAHs) both within and beyond the rhizosphere

Exploitation of mycorrhizas to enhance phytoremediation of organic pollutants has received attention recently due to their positive effects on establishment of plants in polluted soils. Some evidence exist that ectomycorrhizas enhance the degradation of pollutants of low recalcitrance, while less easily degradable polyaromatic molecules have been degraded only by some of these fungi in vitro. Natural polyaromatic (humic) substances are degraded more slowly in soil where ectomycorrhizal fungi are present, thus phytoremediation of recalcitrant pollutants may not benefit from the presence of these fungi. Using a soil spiked with three polycyclic aromatic hydrocarbons (PAHs) and an industrially polluted soil (1 g kg(-1) of summation operator12 PAHs), we show that the ectomycorrhizal fungus Suillus bovinus, forming hydrophobic mycelium in soil that would easily enter into contact with hydrophobic pollutants, impedes rather than promotes PAH degradation. This result is likely to be a nutrient depletion effect caused by fungal scavenging of mineral nutrients.     

Identification of a new Irgarol-1051 related s-triazine species in coastal waters

A previously unknown s-triazine species present in commercially available Irgarol-1051, a booster biocide additive in copper-based antifouling paints for the replacement of organotin-based antifoulants, has been identified in the coastal aquatic environment. After careful isolation, purification and characterization by high resolution MS-MS and (1)H NMR, the molecular structure of that unknown species is found to be N,N'-di-tert-butyl-6-methylthiol-s-triazine-2,4-diamine (designated as M3). Levels of Irgarol-1051, its major degradation product (M1) and the newly identified M3 in the coastal waters of Hong Kong, one of the world's busiest ports located in the southern coast of China, were monitored by SPME-GC-MS and SPME-GC-FID. Water samples from five locations within Hong Kong waters were analysed and the levels of Irgarol-1051, M1 and M3 were found to be 0.1-1.6 microg l(-1), 36.8-259.0 microg l(-1) and 0.03-0.39 microg l(-1), respectively. Our results indicate that M3 is relatively stable against photo- and bio-degradation and may pose considerable risk to primary producer communities in the coastal marine environment.     

Risk to breeding success of waterbirds by contaminants in Hong Kong: evidence from trace elements in eggs

Concentrations of 17 trace elements (As, Se, Rb, Sr, Ag, Sb, Cs, Tl, Pb, V, Cr, Mn, Co, Cu, Zn, Cd, and Hg) were determined in eggs of little egrets (Egretta garzetta), black-crowned night herons (Nycticorax nycticorax) and bridled terns (Sterna anaethetus) from northwestern and northeastern coastal areas of Hong Kong. Results indicated significant differences among the three species. Eggs of little egrets and black-crowned night herons appeared to be good bioindicators for monitoring selected elements (As, Pb, Zn Cr, Cu, and V) due to consistent correlations between metal concentrations in eggs and those in coastal marine sediments. Based on limited toxicological information, the predicted no effect concentrations (PNECs) of Hg and Se in the bird eggs were estimated as 0.5 to 1.8 and 0.90 to 1.45 mug g(-1), dry wt., respectively. Hazard quotients (HQs) indicated that Hg and Se might pose some risk to certain waterbirds in Hong Kong.     

Risk assessment for human consumption of perfluorinated compound-contaminated freshwater and marine fish from Hong Kong and Xiamen

Perfluorinated compounds (PFCs) are man-made fluoro-surfactants that are identified as global pollutants and can pose health risks to humans and wildlife. Two aspects of risk assessment were conducted in this study, including exposure and response. Exposure was estimated by using the concentrations of PFCs in fish and applying standard exposure factors. Among different PFCs, PFOS, PFOA, PFNA, PFDA, PFUdA and PFTrDA were detected. Total concentrations of PFC in fish ranged from 0.27-8.4 ng g⁻¹ to 0.37-8.7 ng g⁻¹ respectively in Hong Kong and Xiamen. The calculated hazard ratio (HR) of PFOS for all fish was less than 1.0. However, the HR for mandarin fish in Hong Kong and bighead carp, grass carp and tilapia in Xiamen, had HR values of approximately 0.5, indicating that frequent consumption of these 4 more contaminated fish species might pose an unacceptable risk to human health. Our data support the notion that the released/disposed chemical pollutants into water systems make fish a source of environmental toxicants to humans. The risks and potential effects of PFCs to health of coastal population in the Pearl River Delta are of concern.     

Assessing copper thresholds for phytotoxicity and potential dietary toxicity in selected vegetable crops

Copper pollution in soils is widespread, and its accumulation in crop products could pose a risk on human health. In this paper, bioavailability of added copper (Cu) and critical Cu concentrations in a vegetable garden soil was evaluated for Chinese cabbage (Brassica chinensis L.), pakchoi (Brassica chinensis L.), and celery (Apiumg graveolens L. var. dulce DC) based on human dietary toxicity. The availability of added Cu in the soil decreased with incubation time, and had minimal change after 10-12 weeks. After incubated for 12 weeks, about 60% of added Cu was not extractable by DTPA. The same crops were also grown in sand culture to determine their responses to solution Cu. Shoot growth was significantly inhibited at Cu concentrations above 10 mg kg(-1) in the solution or above 150 mg kg(-1) (DTPA-Cu) in the soil. The sensitivity of the crops to Cu toxicity differed among the three vegetable crops. Copper concentration in shoots and edible parts varied with Cu supply levels and type of the vegetables. Negative correlations (r=-0.90-0.99**) were noted between Cu concentration in shoots and fresh matter yields, but Cu concentrations in the edible parts were positively correlated with available and total Cu in the soil (r=0.91-0.99**). The critical tissue Cu concentrations at 10% shoot DM reduction were 19.4, 5.5, 30.9 mg kg(-1) for Chinese cabbage, pakchoi, and celery, respectively. Based on the threshold of human dietary toxicity for Cu (10 mg kg(-1)), the critical concentrations of total and available Cu in the soil were 430 and 269 mg kg(-1) for pakchoi, 608 and 313 mg kg(-1) for celery, and 835 and 339 mg kg(-1) for Chinese cabbage, respectively.     

Polychlorinated biphenyls and organochlorine pesticides in local waterbird eggs from Hong Kong: risk assessment to local waterbirds

The contamination status of the marine environment in Hong Kong was studied by measuring concentrations of organochlorine (OC) pollutants (i.e., hexachlorobenzene, aldrin, dieldrin, endrin, mirex, total heptachlor, total chlordane, total DDTs, total PCBs, and total toxaphenes) in the eggs of selected waterbird species from different locations around the city: Little Egret (Egretta garzetta) and Chinese Pond Heron (Ardeola bacchus) from Mai Po Village, Great Egret (Ardea alba) and Black-crowned Night Heron (Nycticorax nycticorax) from A Chau, and Chinese Pond Heron (A. bacchus) from Ho Sheung Heung. The mean concentrations of total PCBs and total DDTs ranged from 191-11 100 ng g⁻¹ lipid and 453-49 000 ng g⁻¹ lipid, respectively. Recent exposure of waterbirds to technical chlordane was found in Hong Kong. The risk characterization demonstrated potential risks to birds associated with exposure to DDE, which was found to cause a reduction in survival of young in Hong Kong Ardeids based on the endpoint in the risk assessment.