Persistent organic pollutants associate with liver disease in a Finnish general population sample

BACKGROUND AND AIMS

Persistent organic pollutants (POPs) have multiple adverse effects on human health. Recent studies show a possible association with liver disease, but population-based data are scarce. In this population-based study, we studied the associations between POPs and biomarkers of liver disease and incident liver disease.

METHODS

This study consisted of 2789 adults that participated in the environmental toxin subset of the Finnish health-examination survey, FINRISK 2007. Toxins were measured from serum samples, and standard liver tests and dynamic aspartate aminotransferase-alanine aminotransferase ratio (dAAR) were measured as biomarkers of liver function. Associations between POPs and the biomarkers were then analysed using linear regression. Associations between POPs and incident liver disease (n = 36) were analysed by Cox regression.

RESULTS

Organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs) and several perfluorinated alkyl substances exhibited statistically significant positive associations with several biomarkers of liver injury (betacoefficient per SD 0.04-0.14, p < 0.05). These associations were stronger in subgroups of individuals with obesity or non-alcoholic fatty liver disease. OCPs, PCBs and perfluoro-octanoic acid also had significant positive associations with dAAR, which can be used to predict risk of incident severe liver outcomes (beta coefficient per SD 0.05-0.08, p < 0.05). OCPs and PCBs were also significantly and positively associated with incident liver disease (hazard ratio per SD 1.82 95% CI 1.21-2.73, p < 0.01 and hazard ratio per SD 1.69, 95% CI 1.07-2.68, p < 0.05 respectively).

CONCLUSIONS

Several POPs show positive associations with markers of liver injury and incident liver disease, suggesting that environmental toxins are important risk factors for chronic liver disease.

Follicular fluid and blood levels of persistent organic pollutants and reproductive outcomes among women undergoing assisted reproductive technologies

Persistent organic pollutants (POPs) are industrial chemicals resistant to degradation and have been shown to have adverse effects on reproductive health in wildlife and humans. Although regulations have reduced their levels, they are still ubiquitously present and pose a global concern. Here, we studied a cohort of 185 women aged 21-43 years with a median of 2 years of infertility who were seeking assisted reproductive technology (ART) treatment at the Carl von Linné Clinic in Uppsala, Sweden. We analyzed the levels of 9 organochlorine pesticides (OCPs), 10 polychlorinated biphenyls (PCBs), 3 polybrominated diphenyl ethers (PBDEs), and 8 perfluoroalkyl substances (PFASs) in the blood and follicular fluid (FF) samples collected during ovum pick-up. Impact of age on chemical transfer from blood to FF was analyzed. Associations of chemicals, both individually and as a mixture, to 10 ART endpoints were investigated using linear, logistic, and weighted quantile sum regression, adjusted for age, body mass index, parity, fatty fish intake and cause of infertility. Out of the 30 chemicals, 20 were detected in more than half of the blood samples and 15 in FF. Chemical transfer from blood to FF increased with age. Chemical groups in blood crossed the blood-follicle barrier at different rates: OCPs > PCBs > PFASs. Hexachlorobenzene, an OCP, was associated with lower anti-Müllerian hormone, clinical pregnancy, and live birth. PCBs and PFASs were associated with higher antral follicle count and ovarian response as measured by ovarian sensitivity index, but also with lower embryo quality. As a mixture, similar findings were seen for the sum of PCBs and PFASs. Our results suggest that age plays a role in the chemical transfer from blood to FF and that exposure to POPs significantly associates with ART outcomes. We strongly encourage further studies to elucidate the underlying mechanisms of reproductive effects of POPs in humans.

Distribution of perfluoroalkyl acids in fish species from the Baltic Sea and freshwaters in Finland

Occurrence and distribution of perfluoroalkyl acids (PFAAs), a sub-category of per- and polyfluoroalkyl substances (PFASs), is widespread in the environment. Food, especially fish meat, is a major pathway via which humans are exposed to PFAAs. As fish is an integral part of Nordic diet, therefore, in this study, several fish species, caught in selected Baltic Sea basins and freshwater bodies of Finland, were analysed for PFAAs. Perfluorooctane sulfonate (PFOS) was detected in all Baltic Sea fish samples and in >80% fish samples from freshwaters. PFOS contributed between 46 and 100% to the total PFAA concentration in Baltic Sea fish samples and between 19 and 28% in fish samples from freshwaters. Geographically, concentration ratios of PFOS to other PFAAs differed between fish from the Baltic Sea and Finnish lakes suggesting that distribution of PFAAs differ in these environments. Results were compared with current safety thresholds - environmental quality standard for biota (EQS_biota) set by the European Commission and a group tolerable weekly intake (TWI) for the sum of four PFASs (∑PFAS-4) i.e. perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorohexane sulfonate (PFHxS) and PFOS, recommended by the European Food Authority (EFSA). EQS_biota compliance was observed for PFOS in all species except smelt caught in the Baltic Sea and also in the River Aurajoki, where smelt had migrated from the Baltic Sea for spawning. Moderate consumption of most Baltic fishes (200 g week^-1) results in an exceedance of the new TWI (4.4 ng kg^-1 body weight week^-1) for ∑PFAS-4.

Mixtures of persistent organic pollutants are found in vital organs of late gestation human fetuses

Persistent organic pollutants (POPs) are industrial chemicals with long half-lives. Early life exposure to POPs has been associated with adverse effects. Fetal exposure is typically estimated based on concentrations in maternal serum or placenta and little is known on the actual fetal exposure. We measured the concentrations of nine organochlorine pesticides (OCPs), ten polychlorinated biphenyl (PCB) congeners, and polybrominated diphenyl ether (PBDE) congeners by gas chromatography - tandem mass spectrometry in maternal serum, placenta, and fetal tissues (adipose tissue, liver, heart, lung and brain) in 20 pregnancies that ended in stillbirth (gestational weeks 36-41). The data were combined with our earlier data on perfluoroalkyl substances (PFASs) in the same cohort (Mamsen et al. 2019). HCB, p,p'-DDE, PCB 138 and PCB 153 were quantified in all samples of maternal serum, placenta and fetal tissues. All 22 POPs were detected in all fetal adipose tissue samples, even in cases where they could not be detected in maternal serum or placenta. Tissue:serum ratios were significantly higher in later gestations, male fetuses, and pregnancies with normal placental function. OCPs showed the highest tissue:serum ratios and PFAS the lowest. The highest chemical burden was found in adipose tissue and lowest in the brain. Overall, all studied human fetuses were intrinsically exposed to mixtures of POPs. Tissue:serum ratios were significantly modified by gestational age, fetal sex and placental function. Importantly, more chemicals were detected in fetal tissues compared to maternal serum and placenta, implying that these proxy samples may provide a misleading picture of actual fetal exposures.

Persistent organic pollutants and the size of ovarian reserve in reproductive-aged women

Industrial chemicals such as persistent organic pollutants (POPs) have been associated with reduced fertility in women, including longer time-to-pregnancy (TTP), higher odds for infertility, and earlier reproductive senescence. Fertility is highly dependent on the ovarian reserve, which is composed of a prenatally determined stock of non-growing follicles. The quantity and quality of the follicles decline with age, thereby eventually leading to menopause. In the clinical setting, assessing ovarian reserve directly through the histological analysis of follicular density in ovaries is not practical. Therefore, surrogate markers of ovarian reserve, such as serum anti-Müllerian hormone (AMH) are typically used. Here, we studied associations between chemical exposure and ovarian reserve in a cohort of pregnant women undergoing elective caesarean section (n = 145) in Stockholm, Sweden. Full data (histological, clinical, serum) were available for 50 women. We estimated the size of the reserve both directly by determining the density of follicles in ovarian cortical tissue samples, and indirectly by measuring AMH in associated serum samples. Concentrations of 9 organochlorine pesticides (OCPs), 10 polychlorinated biphenyls (PCBs), 3 polybrominated diphenylethers (PBDEs) and 9 perfluoroalkyl substances (PFAS) were determined in serum, and clinical data were retrieved from electronic medical records. Healthy follicle densities (median 0, range 0-193 follicles/mm³) and AMH levels (median 2.33 ng/mL, range 0.1-14.8 ng/mL) varied substantially. AMH correlated with the density of growing follicles. Twenty-three chemicals detected in more than half of the samples were included in the analyses. None of the chemicals, alone or as a mixture, correlated with AMH, growing or atretic follicles. However, HCB, transnonachlor, PCBs 74 and 99 were associated with decreased non-growing follicle densities. HCB and transnonachlor were also negatively associated with healthy follicle density. Further, mixture of lipophilic POPs (PBDE 99, p,p'-DDE, and PCB 187) was associated with lower non-growing follicle densities. In addition, exposure to HCB, p,p'-DDE, and mixture of OCPs were significantly associated with higher odds of infertility. The results suggest that exposure to chemicals may reduce the size of ovarian reserve in humans, and strongly encourage to study mechanisms behind POP-associated infertility in women in more detail.

Persistent organic pollutants, pre-pregnancy use of combined oral contraceptives, age, and time-to-pregnancy in the SELMA cohort

BACKGROUND

We are exposed to several chemicals such as persistent organic pollutants (POPs) in our everyday lives. Prior evidence has suggested that POPs may have adverse effects on reproductive function by disrupting hormone synthesis and metabolism. While there is age-related decline of fertility, the use of hormonal combined oral contraceptives (COCs) and its association to return of fertility remains controversial. The goal of this study is to investigate the association between exposure to POPs, both individually and as a mixture, and fecundability measured as time-to-pregnancy (TTP) according to pre-pregnancy use of COCs and age.

METHODS

Using the SELMA (Swedish Environmental Longitudinal Mother and Child, Allergy and Asthma) study, we have identified 818 pregnant women aged 18-43 years (mean 29 years) with data on how long they tried to get pregnant and what was their most recently used contraceptive method. These data were collected at enrollment to the study (median week 10 of pregnancy). Concentrations of 22 POPs and cotinine were analyzed in the blood samples collected at the same time as the questions on TTP and pre-pregnancy use of contraceptive. Analyses were done on the association between POPs exposure and TTP measured as continuous (months) and binary (infertile for those with TTP > 12 months). To study the chemicals individually, Cox regression and logistic regression were used to estimate fecundability ratios (FRs) and odds ratios (ORs), respectively. Weighted quantile sum (WQS) regression was used to investigate the chemicals as a mixture where chemicals of concern were identified above the 7.6% threshold of equal weights. To perform the subgroup analysis, we stratified the sample according to use of COCs as the most recent pre-pregnancy contraception method and age (< 29 years, and ≥ 29 years). The models were adjusted for parity, regularity of menses, maternal body mass index (BMI) and smoking status, and stratified as described above.

RESULTS

Prior to stratification, none of the POPs were associated with fecundability while increased exposure to HCB, PCB 74 and 118 had higher odds of infertility. Upon stratification, POP exposure was significantly associated with longer TTP in women aged ≥29 years who did not use COC. Specifically, PCBs 156, 180, 183, and 187 were associated with reduced fecundability while PCBs 99, 153, 156, 180, 183, and 187 had higher odds of infertility. As a mixture, we identified the chemicals of concern for a longer TTP include PCBs 118, 156, 183, and 187. Moreover, chemicals of concern identified with increased odds of infertility were PCB 74, 156, 183, 187, and transnonachlor.

CONCLUSION

Serum concentrations of selected POPs, both as individual chemicals and as a mixture, were significantly associated with lower fecundability and increased odds of infertility in women aged 29 years and above not using COC as their most recent pre-pregnancy contraceptive. Our findings suggest that pre-pregnancy use of oral contraceptive and age may modify the link between POPs and fecundability. The differences of specific chemicals in the individual analysis and as a mixture support the need to study combination effects of chemicals when evaluating reproductive outcomes.

Human exposure to PCDDs and their precursors from heron and tern eggs in the Yangtze River Delta indicate PCP origin

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are highly toxic to humans and wildlife. In the present study, PCDD/Fs were analyzed in the eggs of whiskered terns (Chlidonias hybrida), and genetically identified eggs from black-crowned night herons (Nycticorax nycticorax) sampled from two lakes in the Yangtze River Delta area, China. The median toxic equivalent (TEQ) of PCDD/Fs were 280 (range: 95-1500) and 400 (range: 220-1100) pg TEQ g^-1 lw (WHO, 1998 for birds) in the eggs of black-crowned night heron and whiskered tern, respectively. Compared to known sources, concentrations of PCDDs relative to the sum of PCDD/Fs in bird eggs, demonstrated high abundance of octachlorodibenzo-p-dioxin (OCDD), 1,2,3,4,6,7,8-heptaCDD and 1,2,3,6,7,8-hexaCDD indicating pentachlorophenol (PCP), and/or sodium pentachlorophenolate (Na-PCP) as significant sources of the PCDD/Fs. The presence of polychlorinated diphenyl ethers (PCDEs), hydroxylated and methoxylated polychlorinated diphenyl ethers (OH- and MeO-PCDEs, known impurities in PCP products), corroborates this hypothesis. Further, significant correlations were found between the predominant congener CDE-206, 3'-OH-CDE-207, 2'-MeO-CDE-206 and OCDD, indicating a common origin. Eggs from the two lakes are sometimes used for human consumption. The WHO health-based tolerable intake of PCDD/Fs is exceeded if eggs from the two lakes are consumed regularly on a weekly basis, particularly for children. The TEQs extensively exceed maximum levels for PCDD/Fs in hen eggs and egg products according to EU legislation (2.5 pg TEQ g^-1lw). The results suggest immediate action should be taken to manage the contamination, and further studies evaluating the impacts of egg consumption from wild birds in China. Likewise, studies on dioxins and other POPs in common eggs need to be initiated around China.

Biomonitoring of selected persistent organic pollutants (PCDD/Fs, PCBs and PBDEs) in Finnish and Russian terrestrial and aquatic animal species

BACKGROUND

The Finnish and Russian animal species (semi-domesticated reindeer, Finnish wild moose, Baltic grey seal and Baltic herring) samples were biomonitored in terrestrial and aquatic environments for polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs) and polybrominated diphenylethers (PBDEs).

RESULTS

Grey seal (Halichoerus grypus) was clearly the most contaminated species. The mean PBDE concentration in grey seal was 115 ng/g fat, and the highest WHO-PCDD/F-PCB-TEQ (toxic equivalent set by WHO) was 327 pg/g fat. In Finnish, reindeer WHO-PCDD/F-TEQ varied from 0.92 pg/g fat in muscle to 90.8 pg/g fat in liver. WHO-PCDD/F-TEQ in moose liver samples was in the range of 0.7-4.26 pg/g fat, and WHO-PCB-TEQ in the range of 0.42-3.34 pg/g fat. Overall moose had clearly lower PCDD/F and DL-PCB concentrations in their liver than reindeer.

CONCLUSIONS

Terrestrial animals generally had low POP concentrations, but in reindeer liver dioxin levels were quite high. All Finnish and Russian reindeer liver samples exceeded the EU maximum level [8] for PCDD/Fs (10 pg/g fat), which is currently set for bovine animals.

Temporal trends in the levels of polychlorinated dioxins, -furans, -biphenyls and polybrominated diethyl ethers in bank voles in Northern Finland

Dioxin-like chemicals and brominated flame retardants are ubiquitous in the environment, despite the introduction of international prohibitions and restrictions. These chemicals do not remain in the vicinity of their source, instead they can be transported over long distances, in fact even to pristine areas in the northern latitudes. However, there have been rather few time series experiments monitoring the trends in the levels of chlorinated and brominated forms of these chemicals in the environment. In this study, the concentrations of polychlorinated dibenzo-p-dioxins and -furans (PCDDs/Fs), polychlorinated biphenyls (PCBs) and polybrominated diethyl ethers (PBDEs) were measured in the liver and muscle of bank voles (Myodes glareolus) caught in a remote area in Finnish Lapland during 1986-2007. Five time points were selected: years 1986, 1992, 1998, 2003 and 2007. The levels of PCDDs/Fs and PCBs declined from 1986 until 2003 in both females and males, but tended to increase again in 2007. The peak levels of the most abundant PBDE congeners (PBDEs 47, 99, 100 and 153) were measured in 1998 and 2003. These results reveal that the levels of dioxin-like chemicals remain high also in rural areas in Lapland, whereas the concentrations of brominated flame retardants decreased and follow the current restriction prohibitions.

Levels and congener profiles of PBDEs in edible Baltic, freshwater, and farmed fish in Finland

Fish is the major source of polybrominated diphenyl ethers (PBDEs) for Finnish consumers. To estimate the PBDE contamination in fish that Finns regularly consume as food, a large-scale sampling was undertaken in 2009-2010. Altogether 207 samples of 17 edible fish species were collected from commercially and recreationally important fishing areas in the Baltic Sea, freshwater lakes, and farming facilities. The analysis of 15 PBDE congeners was performed in an accredited testing laboratory with high-resolution gas chromatography mass spectrometry. In all of the samples, the Σ15PBDE varied between 0.029 and 73 ng/g fw. The most abundant congeners were BDE-47 (average proportion 42%), -99 (8.4%), -100 (11%), -154 (5.6%), and -209 (27%). High levels of BDE-209 were observed in the Baltic Sea, off the coast of Pori, in Baltic herring, perch, pike, and pike-perch. Overall, the PBDE levels in Baltic and freshwater fish were low. The levels in farmed whitefish were slightly higher than in wild whitefish. The reasons for the high BDE-209 levels in Baltic herring in Pori and the elevated levels of PBDEs in farmed whitefish should be investigated more thoroughly.

Time trends and congener profiles of PCDD/Fs, PCBs, and PBDEs in Baltic herring off the coast of Finland during 1978-2009

In Finland, consumption of Baltic fatty fish may lead to high exposure to persistent organic pollutants (POPs), which might have hazardous health effects. Monitoring of POPs in Baltic fish enables the health authorities to keep dietary advice on fish consumption up to date. In this study, which is a compilation of analytical data from earlier studies, time trends and congener profiles of polychlorinated dioxins and furans (PCDD/Fs) and biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs) in Baltic herring are reported. Altogether 344 samples of Baltic herring from 1978-2009 were collected across the Finnish coast of the Baltic Sea. The chemical analysis was performed in an accredited testing laboratory with high resolution gas chromatography mass spectrometry. During the 31-year period, PCDD/F and PCB concentrations decreased on approximately 80%, from approximately 20 to 5 pg/g fw, expressed as WHO2005 TEQ. The PBDE concentrations experienced a 4-10 fold increase during late 1980s-early 1990s, and declined to 1978s levels of approximately 2 ng/g fw by 2009. The current concentrations of PCDD/Fs, PCBs and PBDEs in Baltic herring are relatively low, and mostly below EU maximum accepted levels, and are expected to continue decreasing. In the future, it may be possible to re-evaluate the consumption restrictions for this specific Baltic fatty fish.

PCDD/Fs, PCBs and PBDEs in zooplankton in the Baltic Sea - spatial and temporal shifts in the congener-specific concentrations

In the marine food-webs, zooplankton is a key element in the transfer of persistent organic pollutants to higher trophic levels. We determined the congener-specific concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in offshore zooplankton (size from 0.2 to 20mm) collected in 2001, 2002 and 2010 in the northern and central Baltic Sea. Of the PCDD/Fs, the concentrations of 2378-TCDF were from 18 to 47 and of 23478-PeCDF from 7.9 to 29 pg g(-1)fat and showed little temporal differences. However, 1234678-HpCDF and OCDF were abundant in 2001-2002 especially in the eastern Gulf of Finland (average concentrations 50 and 89 pg g(-1)fat, respectively). In 2010 the concentrations of these two congeners were lower, 29 and 30 pg g(-1)fat, respectively, but still substantially higher than in the other surveyed areas. The principal components analysis (PCA) supported that area-specific patterns in pollution strongly contributed to the congener profiles particularly in surface sediment and in sediment trap material, but even in zooplankton. The concentrations of the PCBs were highest in the Gulf of Finland and in the Bothnian Bay. The concentrations of most PCBs were somewhat lower in 2010 than in 2001-2002. Of the dioxin-like PCBs, the concentrations of PCB-77 were highest (271-572 pg g(-1)fat) but PCB-126 (32-113 pg g(-1)fat) contributed from 85% to 91% of the total toxicity of PCBs due to its higher toxic potency. Of the PBDEs, the BDE47 and BDE99 were the most abundant (concentrations from 1.2 to 4.6 and from 0.4 to 3.3 ng g(-1) fat, respectively). The concentrations of most PBDEs were lower in 2010 than in 2001/2002 except in the eastern Gulf of Finland.

Persistent organic pollutant levels in semi-domesticated reindeer (Rangifer tarandus tarandus L.), feed, lichen, blood, milk, placenta, foetus and calf

A study concerning persistent organic pollutants in Finnish semi-domesticated reindeer was conducted in northern Finland. The aim of this study was to explore POP presence in different tissues of reindeer. In addition, it was studied how POPs are transported from food concentrates and lichen to reindeer hind tissues and further to the placenta, foetus, milk and calf. Concentrations of 17 polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/Fs), 37 polychlorinated biphenyls (PCBs) (including 12 dioxin-like PCBs), and 15 polybrominated diphenyl ethers (PBDEs) were analysed. In most of the reindeer muscle tissue samples PCBs were clearly dominating compounds (on average 58% of the total WHO-TEQ). The total WHO-TEQ was higher in the muscle tissue of reindeer calves than in their corresponding hinds (on average 1.7 pg/g fat vs. 1.1 pg/g fat, respectively). The total WHO-TEQ concentrations were higher in the muscle and liver tissues of reindeer hinds than in their blood or placentas. The foetuses had clearly lower WHO-TEQ concentrations than their corresponding hinds. The contribution of WHO-PCDD/F-TEQ to the total WHO-TEQ was somewhat higher in the liver than in the muscle tissue. The reindeer hind-calf pair, which had gone through the lichen diet, had on average higher WHO-PCDD/F- and PCB-TEQ concentrations in their tissues than the hind-calf-pair that had gone through the reindeer food concentrate diet. WHO-PCB-TEQs in the reindeer foetuses were equal with the concentrations of placentas. The reindeer foetuses contained generally more PBDEs than their corresponding hinds and placentas. This may indicate effective transport of these compounds through the placenta of reindeer.

Sedimentation of PCDD/Fs and PCBs in the Gulf of Finland and the Gulf of Bothnia, the Baltic Sea

Sediment trap material was collected during May-December in the period 1996-2008 in three coastal areas and four open sea stations in the Finnish territory of the Baltic Sea. The highest sedimentation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) with a typical source-related congener profile from chlorophenol production dominated by highly chlorinated dibenzofurans was found close to a historical source in the Kymijoki estuary. This was an order of magnitude higher than in other river estuaries and two orders of magnitude higher than in the open sea stations. The sedimentation of polychlorinated biphenyls (PCBs) was also higher in river estuaries than in other areas. No significant decrease over a 12 year period of monitoring was found in concentration or in sedimentation in the Kymijoki estuary. In the western Gulf of Finland, the Archipelago Sea and the Gulf of Bothnia, the dominating congeners, calculated as toxic equivalent (TEQ) in sedimentation were 1, 2, 3, 7, 8-PeCDD and 2, 3, 4, 7, 8-PeCDF, often reported as the main congeners in deposition.

Levels of PCDD/Fs, PCBs and PBDEs in breast milk of women living in the vicinity of a hazardous waste incinerator: assessment of the temporal trend

The concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) were determined in breast milk from women living in the vicinity of a hazardous waste incinerator (HWI) in Catalonia, Spain. The results were compared with the levels obtained in previous surveys carried out in the same area in 1998 (baseline study), 2002 and 2007. The current total concentrations of 2,3,7,8-chlorinated PCDD/Fs in breast milk ranged from 18 to 126 pg g(-1)fat (1.1-12. 3 pg WHO2005-TEQPCDD/F), while the total levels of PCBs ranged from 27 to 405 pg g(-1)fat(0.7-5.3 pg WHO2005-TEQPCB). In turn, PBDE concentrations (sum of 15 congeners) ranged 0.3-5.1 g g(-1)fat, with a mean value of 1.3 ng g(-1)fat. A general decrease in the concentrations for PCDD/Fs, both planar and total PCBs, and PBDEs in breast milk was observed. The levels of PCDD/Fs, PCBs, and PBDEs in milk of women living in urban zones were higher than those corresponding to industrial zones (41%, 26%, and 8%, respectively). For PCDD/Fs and PCBs, the current decreases are in accordance with the reduction in the dietary intake of these pollutants that we have also observed in recent studies carried out in the same area of study.

Persistent organic pollutants in Finnish reindeer (Rangifer tarandus tarandus L.) and moose (Alces alces)

Summary

Occurrence of PCDD/F, PCB, PBDE, PFAS, and organotin compounds in fish meal, fish oil and fish feed

We analysed polychlorinated dibenzo-p-dioxins and furans (PCDD/F, dioxins), and polychlorinated biphenyls (PCB) in 13 fish meal, five fish oil, and seven fish feed samples. Polybrominated diphenyl ethers (PBDE), organotin compounds (OTC), and perfluoroalkylated substances (PFAS) were analysed in ten fish meal, two fish oil, and two fish feed samples. All measured TEQ concentrations of PCDD/F and PCB were below the maximum levels set by Directive 2002/32/EC. There was no correlation between concentrations of WHOPCDD/F-TEQ and indicator PCB in our samples. The most common congeners among PBDEs were BDE-47 and BDE-100. BDE-209 was present in five fish meals of the ten analysed. Tributyltin (TBT) was the predominant congener in all samples except in three fish meals, where monobutyltin (MBT) was the major congener. Perfluorooctane sulphonate (PFOS) was the predominant congener in six fish meals of the ten analysed. There was large variation in concentrations and congener distributions of the studied compounds between our samples. Our results underline a need to pay special attention to the origin and purity of feed raw material of marine origin.

Polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs) in Finnish semi-domesticated reindeer (Rangifer tarandus tarandus L.)

To explore the concentrations and dynamics of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in Finnish semi-domesticated reindeer (Rangifer tarandus tarandus L.) the reindeer milk and tissue samples were collected from the sub-arctic northern Finland. Reindeer milk's PCB sum (1.20 ng g(-1) wet weight) and PCDD/F sum (0.70 pg g(-1) ww) in autumn were higher than in summer (PCBs 0.50 ng g(-1) ww and PCDD/Fs 0.20 pg g(-1) ww). The mean fat content in autumn milk (26%) was significantly higher than in summer (10%). Concentrations in reindeer milk were generally far below 50% of that in adult reindeer body burden. However, the bioaccumulation factors were multiple in milk/reindeer calf ratio and that aroused the question of other important exposure routes than lactation. The muscle and liver of reindeer calves had higher PCDD/F and PCB concentrations than adult animals that possibly indicate the significance of transfer of these compounds from dam to calf through lactation and placenta. However, PBDE concentrations were higher in adult reindeer, especially in liver. In addition, reindeer liver seems to have a special feature to collect highly toxic PCDD/Fs, although the PCB sum concentrations (range from 0.33 to 1.69 ng g(-1) wet weight) were clearly higher than the sums of PCDD/Fs (range from 3.78 to 39.2 pg g(-1) ww). Stillborn reindeer calves represented individuals who had got their PCDD/F, PCB and PBDE load only via the placenta. Concentrations in muscle and brown adipose tissue samples did not indicate dependency on fat content. Obviously effective placental transfer of PCBs and PBDEs from reindeer dam to foetus was seen in this study.

Persistent organic pollutants in two Finnish watercourses: levels, congener profiles and source estimation by mussel incubation

Mussel incubation was used to compare two Finnish watercourses, which have been contaminated by effluents from pulp mills and are known to be polluted with polychlorinated biphenyls (PCBs). Lake mussels (Anodonta Piscinalis) incubated in 1998 and 2004 in the rivers Kymijoki and Vuoksi were analysed for PCBs and polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), naphthalenes (PCNs), diphenyl ethers (PCDEs), hydroxy diphenyl ethers (HO-PCDEs), methoxy diphenyl ethers (MeO-PCDEs), and polybrominated diphenyl ethers (PBDEs). The contamination of the River Kymijoki, which descends to the Baltic Sea, proved significantly greater than that of the River Vuoksi, with no decreasing apparent trend, except for the PBDEs. The River Vuoksi represented more a background area compared to the River Kymijoki, excluding the PCBs. The concentration of the PCDD/PCDFs in the Kymijoki mussels exceeded the EU's maximum permissible level for PCDD/PCDFs in foodstuffs (4 pg g(-1) fresh weight). Analyses of perfluorooctanesulphonate and perfluorooctanoate in the mussels incubated in 2005 and 2006 in the River Kymijoki revealed no significant contamination of the river with these compounds. Comparison of the data of the mussels with that of sediments and commercial formulations showed that the past manufacture of a chlorophenol-based wood preservative has remained a significant source of the PCDD/PCDFs, HO-PCDEs and PCDEs in the River Kymijoki. PCB formulations are believed to represent the major sources of the PCBs and PCNs in both watercourses, though situation in the River Kymijoki had been influenced by a chlor-alkali plant. Municipal wastewaters are believed to represent the major source of the PBDEs.

Polychlorinated dibenzo-p-dioxins, dibenzofurans, and polychlorinated biphenyls in semi-domesticated reindeer (Rangifer tarandus tarandus) and wild moose (Alces alces) meat in Finland

Semi-domesticated reindeer and wild moose meat samples were analyzed for polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), and polychlorinated biphenyls (PCBs). Both calves and adults were studied. Individual reindeer and moose meat samples and pooled reindeer calf meat samples were collected from the northern, the middle, and the southern reindeer herding regions in Finland. Samples represented the edible parts of carcasses. In individual samples of reindeer the fat based WHO-PCDD/F-PCB-TEQ concentration was on average 3.2pgg(-1) in calves and 2.3pgg(-1) in adults. In moose calves the fat based WHO-PCDD/F-PCB-TEQ concentration (1.9pgg(-1)) was lower than in reindeer calves. WHO-PCDD/F-PCB-TEQ concentration in the adult moose samples was equal as in the adult reindeer samples. The mean fat based WHO-PCDD/F-PCB-TEQ concentration was highest in reindeer calf samples from the middle region. These samples contained also the highest content of fat. Individual samples of reindeer contained on average more WHO-PCB-TEQ than WHO-PCDD/F-TEQ, while the opposite was true for moose samples, and also samples of adult reindeer from the southern area. The contributions of PCDD/Fs and PCBs to the total TEQ were similar in the reindeer calves' pooled samples which were collected from more western regions than individual samples.

Concentrations of PCDD/Fs, PCBs and PBDEs in breast milk of women from Catalonia, Spain: a follow-up study

The concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs) were determined in breast milk from women living in the vicinity of a new hazardous waste incinerator (HWI) in Catalonia, Spain. The results were compared with the levels obtained in two previous surveys carried out in 1998 (baseline study) and 2002. The current concentrations of PCDD/Fs in breast milk ranged from 45 to 143 pg/g fat (2.8 to 11.2 pg WHO-TEQ/g fat), while total PCBs ranged from 114 to 617 pg/g fat (2.8 to 17.6 pg WHO-TEQ/g fat). PBDE concentrations (sum 15 congeners) ranged from 0.57 ng/g fat to 5.9 ng/g fat, with a mean value of 2.5 ng/g fat. A general decrease of the concentrations for PCDD/Fs and both planar and total PCBs was observed. Regarding to PBDE concentrations in breast milk, similar levels between the 2002 and the present study were noted. The levels of PCDD/Fs and PCBs in milk of women living in urban areas were higher than those corresponding to the industrial zones (38% and 40%, respectively). However, the current PBDE levels were slightly lower (13%) in the urban than in the industrial zone. For PCDD/Fs and PCBs, the current decreases are in accordance with the reduction in the dietary intake of these pollutants found in recent studies carried out in the same area of study.

A decision framework for possible remediation of contaminated sediments in the River Kymijoki, Finland

BACKGROUND, AIM, AND SCOPE

The paper describes the spatial contamination of the River Kymijoki, South-Eastern Finland, and the coastal region of the Gulf of Finland with PCDD/Fs and mercury. The findings of ecotoxicologial and human health studies are also reported, including environmental and human risk assessments. Sediments from the River Kymijoki, draining into the Gulf of Finland, have been heavily polluted by the pulp and paper industry and by chemical industries. A wood preservative, known as Ky-5, was manufactured in the upper reaches of the river between 1940 and 1984 causing severe pollution of river sediments with polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF). Moreover, the sediments have been polluted with mercury (Hg) from chlor-alkali production and the use of Hg as a slimicide in pulp and paper manufacturing.

MATERIALS AND METHODS

An extensive sediment survey was conducted as well as sediment transport modeling, toxicity screening of sediment invertebrates, and a survey of contaminant bioaccumulation in invertebrates and fish. Studies on human exposure to PCDD/Fs and the possible effects on hypermineralization of teeth as well as an epidemiological study to reveal increased cancer risk were also conducted. An assessment of the ecological and human health risks with a null hypothesis (no remediation) was undertaken.

RESULTS

The sediment survey revealed severe contamination of river and coastal sediments with PCDD/Fs and Hg. The total volume of contaminated sediments was estimated to reach 5x10(6) m3 and hot spots with extremely high concentrations (max 292,000 ng g(-1) or 1,060 ng I-TEQ g(-1) d.w.) were located immediately downstream from the pollution source (approximately 90,000 m3). Sediment contamination was accompanied by changes in benthic assemblages, but direct effects were masked by many factors. The fish showed only slightly elevated PCDD/F levels in muscle, but orders of magnitude higher in the liver compared with reference freshwater sites and the Baltic Sea. The concentrations in human fat did not reveal high human exposure in the Kymijoki area in general and was lower than in sea fishermen. The relative risk for total cancer among farmers was marginally higher (RR=1.13) among those living close to the river, compared with farmers living further away, and the possibility of increased cancer risk cannot be ruled out. A conservative risk assessment revealed that the present probability of exceeding the WHO upper exposure limit of 4 pg WHO-TEQ kg(-1) d(-1) for PCDD/Fs and DL-PCBs was 6%. The probability of exceeding the WHO limit value of 0.23 mug kg(-1) d(-1) for methyl mercury was estimated to be notably higher at 62%. Based on these studies and the estimated risks connected with different remediation techniques a general remediation plan with cost benefit analysis was generated for several sub-regions in the river. Dredging, on-site treatment, and a close disposal of the most contaminated sediments (90,000 m3) was suggested as the first phase of the remediation. The decision regarding the start of remediation will be made during autumn 2008.

CONCLUSIONS

The sediments in the River Kymijoki are heavily polluted with PCDD/Fs and mercury from earlier chlorophenol, chlor-alkali, and pulp and paper manufacturing. A continuous transport of contaminants is taking place to the Gulf of Finland in the Baltic Sea. The highly increased PCDD/F and Hg levels in river sediments pose an ecotoxicological risk to benthic fauna, to fish-eating predators and probably to human health. The risks posed by mercury exceed those from PCDD/Fs and need to be evaluated for (former) chlor-alkali sites and other mercury releasing industries as one basis for remediation decision making.

RECOMMENDATIONS AND PERSPECTIVES

The studies form the basis of a risk management strategy and a plan for possible remediation of contaminated sediments currently under consideration in the Southeast Finland Regional Environment Centre. It is recommended that a detailed restoration plan for the most seriously contaminated areas should be undertaken. Based on current knowledge, the restoration of the whole river is not feasible, considering the current risk caused by the contaminated sediment in the river and the costs of an extensive restoration project. The experiences gained in the present case should be utilized in the evaluation of PCDD/F- and mercury-contaminated sites in other countries. The case demonstrates that the historic reservoirs are of contemporary relevance and should be addressed, e.g., in the national implementation plans of the Stockholm Convention.

Contamination of River Kymijoki sediments with polychlorinated dibenzo-p-dioxins, dibenzofurans and mercury and their transport to the Gulf of Finland in the Baltic Sea

Kymijoki, the fourth largest river in Finland, has been heavily polluted by pulp mill effluents as well as the chemical industry. Up to 24,000 ton of wood preservative, chlorophenol known as Ky-5, was manufactured in the upper reaches of the river, an unknown amount of which was discharged into the river between 1940 and 1984. Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) occurred as impurities in the final Ky-5 product. The PCDD/F concentrations and burden in the river sediments were studied and the transport of PCDD/Fs from contaminated sites downstream and into the Gulf of Finland in the Baltic Sea was estimated. More than 190 sediment cores were sampled to estimate the volume of contaminated sediments and the total PCDD/F burden. The transport of PCDD/Fs was estimated using sediment traps placed at several sites. The survey revealed that sediments in the river were heavily polluted by PCDD/Fs, the main toxic congener being 1,2,3,4,6,7,8-heptachlorodibenzofuran, a major contaminant in the Ky-5 product. The mean total concentration at the most polluted river site downstream from the main source was 42000 microg kg(-1) d.w. (106 microg I-TEQ kg(-1)). The elevated concentrations in the coastal region and the present estimated transport from the River Kymijoki confirm earlier assessments that the river is a major source of PCDD/F for the Gulf of Finland.

Dioxins in adipose tissue of women in Southern Spain

Seventeen polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) were quantified in adipose tissue samples of non-occupationally exposed women living in Southern Spain. Geometric mean levels of sum of congeners and WHO(PCDD/F)-TEQ(2005) were 410 and 17.9pgg(-1) fat, respectively. Among PCDDs, octachlorodibenzo-p-dioxin (OCDD) showed the highest concentration with a mean value of 265pgg(-1) fat, followed by 1,2,3,6,7,8-HxCDD (49.3pgg(-1) fat) and 1,2,3,4,6,7,8-HpCDD (45.2pgg(-1) fat). These three congeners were responsible for around 90% of the sum of all PCDD/F congeners in adipose tissue. The geometric mean 2,3,7,8-TCDD value was 1.87pgg(-1) fat. 2,3,4,7,8-PeCDF (8.43pgg(-1) fat) showed the highest concentration among the PCDFs, followed by 1,2,3,4,7,8-HxCDF (4.17pgg(-1) fat) and 1,2,3,6,7,8-HxCDF (3.28pgg(-1) fat), and these three congeners were responsible for 4% of the sum of all studied PCDD/F congeners in adipose tissue and 76% of the sum of ten PCDFs. 1,2,3,7,8,9-HxCDF was the only congener not quantified in any sample, while 1,2,3,4,7,8,9-HpCDF, 1,2,3,7,8-PeCDF, OCDF and 2,3,7,8-TCDF were found in 5, 16, 16 and 19 samples, respectively. All other congeners were quantifiable in all 20 samples. Congeners contributing most to the WHO(PCDD/F)-TEQ(2005) were 1,2,3,7,8-PeCDD (31.6%), 1,2,3,6,7,8-HxCDD (28.3%) and 2,3,4,7,8-PeCDF (14.6%). The body burden of log-transformed WHO(PCDD/F)-TEQ(2005) levels increased with age (B=0.02; 95% CI=0.01, 0.03; p=0.02). Although these adipose tissue PCDD/F levels are similar to previously published findings in Spain and other European countries, further research is needed to determine trends in the exposure of women to these chemical residues.

Organohalogen pollutants in herring from the northern Baltic Sea: concentrations, congener profiles and explanatory factors

Organohalogen contaminants were investigated in Baltic herring caught from three catchment areas in the Baltic Sea, off the coasts of Finland. Pools of both small and large herring were analysed for polychlorinated biphenyls (PCB), dibenzo-p-dioxins, dibenzofurans, naphthalenes, camphenes (toxaphene), polybrominated diphenyl ethers and the pesticide DDT and its metabolites. PCB concentrations per fresh weight in small herring were at the same level in all catchment areas, i.e. the Bothnian Bay, the Bothnian Sea and the Gulf of Finland, revealing no hot spots and reflecting most likely long term emissions and atmospheric deposition. Differences in the levels and/or congener profiles of other contaminants between catchment areas may be explained by point sources. Similar concentrations in small and large herring in the Gulf of Finland were possibly due to their common nutrition. In the other areas, differences between small and large herring most likely reflected their different food sources.

Dioxin exposure in contaminated sawmill area: the use of molar teeth and bone of bank vole (Clethrionomys glareolus) and field vole (Microtus agrestis) as biomarkers

Developmental disorders of teeth are among the most sensitive targets of polychlorinated dibenzo-p-dioxin and -furan (PCDD/F) exposure. In rats, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) reduces dose-dependently the size of molars, most severely the third lower molars. Dioxins also have effects on developing bone, including altered bone mineral density as well as reduced bending breaking force and stiffness. The aim of this study was to evaluate the use of the third lower molar and long bones as biomarkers of PCDD/F exposure in two wild vole species, the bank vole (Clethrionomys glareolus) and the field vole (Microtus agrestis) collected from a PCDD/F contaminated former sawmill area. Survey of soil and biota of the sawmill area indicated a PCDD/F contamination with a congener profile characteristic for the chlorophenol wood preservative Ky-5. The PCDD/F concentration in the bank vole was notably higher than in the field vole. The third molar of the bank vole was significantly smaller in dioxin-exposed animals compared to control group, while there was no difference between these two groups in the field vole. No significant alterations were observed in bone density and strength in either species except for reduced bending strength of the femur neck in bank vole males exposed to dioxins. Even though the bone changes are among the sensitive endpoints of dioxin-exposure, high variability due to age, size and gender limits their use as biomarkers of wildlife exposure. In conclusion, the size of molar teeth seems to be a sensitive and robust biomarker for PCDD/F exposure in wild bank vole populations and thus worth of further studies.

Dioxin concentrations in sediments of the Baltic Sea--a survey of existing data

Recent survey results for polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs, dioxins) in Baltic Sea sediments from Finland, Sweden and Denmark were merged with previously published Baltic Sea data. Regional distribution of concentration levels, differences in congener patterns, and temporal changes in sediment profiles were examined. One of the main objectives was to study if any major point sources for different PCDD/F congeners could be identified on a regional scale, based on sediment records. The survey confirmed the impact of chlorophenol production derived highly chlorinated PCDF-congeners on the total toxicity in sediments in the Gulf of Finland near the Kymijoki river estuary. Signatures of other point sources or combined point sources pertinent to specific industry branches or particular production processes (such as pulp bleaching, vinyl chloride production, thermal processes) may be discerned. However, the findings did not support any of the known point sources significantly influencing those congeners that are most abundant in Baltic herring and salmon. Instead, regional distributions in the Baltic Sea indicate that atmospheric deposition may act as a major source for those congeners and especially for 2,3,4,7,8-PeCDF. There were clear indications of declines in levels in sediment in some areas, but generally the levels of highly chlorinated PCDD/Fs on the northern coast of the Gulf of Finland were still high when compared with other areas of the Baltic Sea. Major areas with data gaps cover the south-eastern and eastern coastal regions of the Baltic Proper and the southern Gulf of Finland.

Perspectives on the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans during municipal solid waste (MSW) incineration and other combustion processes

The pathways by which polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) are formed and the interactions between their aromatic precursors, in particular chlorophenols (ClPhs), and transition metal catalysts are discussed. A literature survey and data from pilot-scale combustion experiments allow conclusions to be drawn on the relations between ClPhs and PCDD/Fs in municipal waste incineration and other combustion processes. The results suggest that the ClPh pathway is among the most important for the formation of PCDD/Fs.

Effect of urea on fly ash PCDD/F concentrations in different particle sizes

The effect of urea as an inhibitor for reducing polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/F) concentrations in flue gases was studied in a pilot scale plant, together with the effect on the particle size distribution of these compounds. Total PCDD/F concentrations decreased by a maximum of 74%, the decrease being greatest for the most highly (octa-) chlorinated isomers. The PCDD/F reduction affected all the particle size classes when an adequate amount of urea was used (1% of the fuel input), which indicates that inhibition, unlike formation, is independent of the fly ash particle size distribution.

PCDD/F reduction in incinerator flue gas by adding urea to RDF feedstock

The effect of urea on PCDD/F formation in a pilot incinerator was studied by incinerating urea with refuse-derived fuel (RDF) at three concentrations (0.1%, 0.5% and 1.0%, of the fuel feed). A distinct reduction in both PCDD/F and chlorophenol concentrations could be noticed when urea was introduced into the system. Partial-least-square (PLS) analysis of the data showed the importance of certain chlorophenol isomers as PCDD/F precursors, pointing to the possibility that the impact point of the urea inhibitor could be before the precursor molecules, i.e. chlorophenols, have been formed.

Urea as a PCDD/F inhibitor in municipal waste incineration

Emissions of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from municipal waste incineration have been widely studied because of their extensive toxicity, and many efforts have been made to restrict their emissions. Although a number of chemical compounds have been shown in laboratory-scale tests to inhibit the formation of PCDD/Fs, few have been tested in pilot- or full-scale plants. This work evaluates the effect of urea as a PCDD/F inhibitor in a pilot-scale incinerator that uses refuse-derived fuel (RDF). The decomposition of urea under the test conditions was also studied using detailed kinetic modeling. An aqueous solution of urea was injected into the flue gas stream after the furnace at approximately 730 degrees C, with varied urea concentrations and flue gas residence times used between the furnace and the sampling point. The results demonstrate that urea can successfully inhibit PCDD/F formation in waste incineration if concentrations and injection points are properly adjusted. The kinetic model showed that urea can be rapidly decomposed under appropriate flue gas conditions, indicating that in addition to the urea molecule itself, decomposition products of urea can also be responsible for the reduction of PCDD/F production during incineration.

Toxic chlorinated and polyaromatic hydrocarbons in simulated house fires

Toxic chlorinated hydrocarbons (polychlorinated biphenyls, benzenes and dioxins and furans) and polyaromatic hydrocarbons were examined in combustion gas and deposited soot wipe samples from simulated house fires. Concentrations of these substances were high during the fires, the amounts of polychlorinated dioxins and furans (PCDD/Fs) in the combustion gas varying from 1.0 to >7.2 ng/m3 (I-TEQ) and those of polyaromatic hydrocarbons from 6.4 to 470 mg/m3. Thus large amounts of organic compounds may be released in house fires. As a result, there is a need for careful personal protection of fire-fighters and remediation workers against combustion gases during a fire and on contaminated surfaces after it.

Effect of liquid inhibitors on PCDD/F formation. Prediction of particle-phase PCDD/F concentrations using PLS modelling with gas-phase chlorophenol concentrations as independent variables

Emissions of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) from municipal waste incineration are currently a subject of considerable public concern because of their extreme toxicity. PCDD/F formation in incineration processes is being studied widely, but little work has been done on their inhibition. We studied the effect of two liquid inhibitors, sodium ammonium hydrogen phosphate (NAHF) and urea (H2NCONH2), on PCDD/F formation in the combustion of liquid fuel doped with copper and chlorine using a pilot-scale plant. The inhibitors were injected into the flue gas stream at a temperature of 725 degrees C, whereupon both the chlorophenol and PCDD/F concentrations decreased. Particle-phase PCDD/F concentrations in particular decreased by up to 90% with NAHF and 70% with urea, but gas phase reduction took place only with urea. The results suggest that the formation of PCDD/Fs is hindered in the particle phase at the early stages of the PCDD/F formation chain, probably even before precursors such as chlorophenols have been formed. As a consequence, particle-phase PCDD/F concentrations can be predicted by a PLS (partial least-squares) approach with the gas-phase chlorophenol concentrations as independent variables. The structure and partial charges of Cu(+)-urea complex were calculated by the HF/3-21G basis set.