Optical signatures of single ion tracks in ZnO.

The optical properties of single ion tracks have been studied in ZnO implanted with Ge by combining depth-resolved hyperspectral cathodoluminescence (CL) and photoluminescence (PL) spectroscopy techniques. The results indicate that ZnO is susceptible to implantation doses as low as 108 to 109 cm-2. We demonstrate that the intensity ratio of ionized and neutral donor bound exciton emissions [D+X/D0X] can be used as a tracer for a local band bending both at the surface as well as in the crystal bulk along the ion tracks. The hyperspectral CL imaging performed at 80 K with 50 nm resolution over the regions with single ion tracks permitted direct assessment of the minority carrier diffusion length. The radii of distortion and space charge surrounding single ion tracks were estimated from the 2D distributions of defect-related green emission (GE) and excitonic D+X emission, both normalized with regard to neutral D0X emission, i.e., from the [GE/D0X] and [D+X/D0X] ratio maps. Our results indicate that single ion tracks in ZnO can be resolved up to ion doses of the order of 5 × 109 cm-2, in which defect aggregation along the extended defects obstructs signatures of individual tracks.

Correlated annealing and formation of vacancy-hydrogen related complexes in silicon.

We report on a deep level transient spectroscopy study of annealing kinetics of a deep, vacancy-hydrogen related level, labeled E5*, at 0.42 eV below the conduction band in hydrogen-implanted n-type silicon. The E5* annealing correlates with the formation of another commonly observed vacancy-hydrogen related level, labeled E5, at 0.45 eV below the conduction band. The annealing of E5* and the formation of E5 exhibit first-order kinetics with an activation energy of 1.61 ± 0.07 eV and a pre-factor of ~1013-1014 s-1. The pre-factor indicates a dissociation or structural transformation mechanism. The analysis of electron capture cross-sections for E5* and E5 reveals considerable transition entropies for both states and a temperature dependent capture cross-section for E5*. Two possible identifications of E5* and E5 are put forward. Firstly, E5* can be attributed to V 2H2(-/0) or V 2H3(-/0), which dissociate with the emission of VH (E5). Secondly, E5* and E5 can be assigned to two different configurations of V 3H.

Hydrogen motion in rutile TiO2.

Uniaxial-stress experiments have been performed for the 3287- and 2445-cm-1 local vibrational modes assigned to the positive charge state of interstitial hydrogen [Formula: see text] and deuterium [Formula: see text], respectively, occurring in mono-crystalline rutile TiO2. The onset of the defect alignment under the stress applied perpendicular to the [001] axis is detected at 165 K (185 K), which corresponds to the activation energy of 0.53 eV (0.58 eV) for interstitial hydrogen (deuterium). Based on these findings the diffusion constants of [Formula: see text] and [Formula: see text] along the [001] axis of TiO2 are determined. The experimental data are complemented by density-functional theory calculations and compared with the earlier results on the diffusion of [Formula: see text]/[Formula: see text] at elevated temperatures up to 700 °C. It is found that the activation energy value deduced from our low-temperature stress measurements yields a very good agreement with the high-temperature data, covering a dynamic range of 12 orders of magnitude.

Interface phenomena in magnetron sputtered Cu2O/ZnO heterostructures.

The interface between ZnO and Cu2O has been predicted to be a good candidate for use in thin film solar cells. However, the high predicted conversion efficiency has yet to be fully realized experimentally. To explore the underlying causes of this we investigate the interface between ZnO and Cu2O in magnetron sputtered samples. Two different sample geometries were made: In the first set thin layers of ZnO were deposited on Cu2O (type A), while in the second set the order was reversed (type B). Using x-ray photoelectron spectroscopy (XPS), an intermediate CuO layer was identified regardless of the order in which the Cu2O and ZnO layers were deposited. The presence of a CuO layer was supported by transmission electron microscopy (TEM) results. Changes in the electron hole screening conditions were observed in CuO near the interface with ZnO, manifested as changes in the relative peak-to-satellite ratio and the degree of asymmetric broadness in the Cu 2p peak. The suppression of the Cu 2p satellite characteristic of CuO may cause the CuO presence to be overlooked and cause errors in determinations of valence band offsets (VBOs). For the type A samples, we compare four different approaches to XPS-based determination of VBO and find that the most reliable results are obtained when the thin CuO layer and the altered screening conditions at the interface were taken into account. The VBOs were found to range between 2.5 eV and 2.8 eV. For the B type samples a reduction of the Cu 2p-LMM Auger parameter was found as compared to bulk Cu2O, indicative of quantum confinement in the Cu2O overlayer.

Electronic properties and morphology of copper oxide/n-type silicon heterostructures.

Silicon-based tandem heterojunction solar cells utilizing cuprous oxide (Cu2O) as the top absorber layer show promise for high-efficiency conversion and low production cost. In the present study, single phase Cu2O films have been realized on n-type Si substrates by reactive magnetron sputtering at 400 °C. The obtained Cu2O/Si heterostructures have subsequently been heat treated at temperatures in the 400-700 °C range in Ar flow and extensively characterized by x-ray diffraction (XRD) measurements, transmission electron microscopy (TEM) imaging and electrical techniques. The Cu2O/Si heterojunction exhibits a current rectification of ~5 orders of magnitude between forward and reverse bias voltages. High resolution cross-sectional TEM-images show the presence of a ~2 nm thick interfacial SiO2 layer between Cu2O and the Si substrate. Heat treatments below 550 °C result in gradual improvement of crystallinity, indicated by XRD. At and above 550 °C, partial phase transition to cupric oxide (CuO) occurs followed by a complete transition at 700 °C. No increase or decrease of the SiO2 layer is observed after the heat treatment at 550 °C. Finally, a thin Cu-silicide layer (Cu3Si) emerges below the SiO2 layer upon annealing at 550 °C. This silicide layer influences the lateral current and voltage distributions, as evidenced by an increasing effective area of the heterojunction diodes.

Hydrogen induced optically-active defects in silicon photonic nanocavities.

We demonstrate intense room temperature photoluminescence (PL) from optically active hydrogen- related defects incorporated into crystalline silicon. Hydrogen was incorporated into the device layer of a silicon on insulator (SOI) wafer by two methods: hydrogen plasma treatment and ion implantation. The room temperature PL spectra show two broad PL bands centered at 1300 and 1500 nm wavelengths: the first one relates to implanted defects while the other band mainly relates to the plasma treatment. Structural characterization reveals the presence of nanometric platelets and bubbles and we attribute different features of the emission spectrum to the presence of these different kind of defects. The emission is further enhanced by introducing defects into photonic crystal (PhC) nanocavities. Transmission electron microscopy analyses revealed that the isotropicity of plasma treatment causes the formation of a higher defects density around the whole cavity compared to the ion implantation technique, while ion implantation creates a lower density of defects embedded in the Si layer, resulting in a higher PL enhancement. These results further increase the understanding of the nature of optically active hydrogen defects and their relation with the observed photoluminescence, which will ultimately lead to the development of intense and tunable crystalline silicon light sources at room temperature.

Impurity sublattice localization in ZnO revealed by Li marker diffusion.

Sublattice localization of impurities in compound semiconductors, e.g., ZnO, determines their electronic and optical action. Despite that the impurity position may be envisaged based on charge considerations, the actual localization is often unknown, limiting our understanding of the incorporation and possible doping mechanisms. In this study, we demonstrate that the preferential sublattice occupation for a number of impurities in ZnO can be revealed by monitoring Li diffusion. In particular, using ion implantation, the impurity incorporation into the Zn sublattice (holds for, B, Mg, P, Ag, Cd, and Sb) manifests in the formation of Li-depleted regions behind the implanted one, while Li pileups in the region of the implantation peaks for impurities residing on O sites, e.g., N. The behavior appears to be of general validity and the phenomena are explained in terms of the apparent surplus of Zn and O interstitials, related to the lattice localization of the impurities. Furthermore, Cd+O and Mg+O co-doping experiments revealed that implanted O atoms act as an efficient blocking "filter" for fast diffusing Zn interstitials.

Negative-U system of carbon vacancy in 4H-SiC.

Using electron paramagnetic resonance (EPR), energy levels of the carbon vacancy (V(C)) in 4H-SiC and its negative-U properties have been determined. Combining EPR and deep-level transient spectroscopy we show that the two most common defects in as-grown 4H-SiC--the Z(1/2) lifetime-limiting defect and the EH(7) deep defect--are related to the double acceptor (2-|0) and single donor (0|+) levels of V(C), respectively.

Formation of donor and acceptor states of the divacancy-oxygen centre in p-type Cz-silicon.

The formation of the divacancy-oxygen centre (V(2)O) in p-type Czochralski-grown silicon has been investigated by means of deep level transient spectroscopy (DLTS). The donor state (+/0) of V(2)O is located at ~E(v) + 0.23 eV (E(v) denotes the valence band edge) and emerges during heat treatment above 200 °C at the expense of the divacancy centre (V(2)). A concurrent transition takes place between the single-acceptor states of V(2) and V(2)O, as unveiled by the injection of electrons through optical excitation during the trap filling sequence of the DLTS measurements. Further, a defect with an energy level at ~E(v) + 0.09 eV evolves in close correlation with the growth of V(2)O but at a factor of ~5-6 lower in concentration. In the literature, the E(v) + 0.09 eV level has previously been attributed to a double-donor state of V(2)O but this assignment can be ruled out by the present data favouring a complex formed between migrating V(2) centres and a competing interstitial oxygen trap. In addition, a level at ~E(v) + 0.24 eV occurs also during the heat treatment above 200 °C and is tentatively assigned to the trivacancy-oxygen centre (V(3)O).

Phase stability and pressure-induced structural transitions at zero temperature in ZnSiO(3) and Zn(2)SiO(4).

Using density functional total energy calculations the structural phase stability and pressure-induced structural transition in different polymorphs of ZnSiO(3) and Zn(2)SiO(4) have been studied. Among the considered monoclinic phase with space groups (P 2(1)/c) and (C 2/c), rhombohedral [Formula: see text] and orthorhombic (Pbca) modifications the monoclinic phase (P 2(1)/c) of ZnSiO(3) is found to be the most stable one. At high pressure monoclinic ZnSiO(3) (C 2/c) can co-exist with orthorhombic (Pbca) modification. Differences in equilibrium volume and total energy of these two polymorphs are very small, which indicates that it is relatively easier to transform between these two phases by temperature, pressure or chemical composition. It can also explain the experimentally established result of metastability of the orthorhombic phase under all conditions. The following sequence of pressure-induced structural phase transitions is found for ZnSiO(3) polymorphs: monoclinic [Formula: see text] monoclinic [Formula: see text] rhombohedral [Formula: see text]. Among the rhombohedral ([Formula: see text]), tetragonal [Formula: see text], orthorhombic (Pbca), orthorhombic (Imma), cubic [Formula: see text] and orthorhombic (Pbnm) modifications of Zn(2)SiO(4), the rhombohedral phase is found to be the ground state. For this chemical composition of zinc silicate the following sequence of structural phase transitions is found: rhombohedral [Formula: see text] tetragonal [Formula: see text] orthorhombic [Formula: see text] orthorhombic (Imma) [Formula: see text] cubic [Formula: see text] orthorhombic (Pbnm). Based on the analogy of crystal structures of magnesium and zinc silicates and using the lattice and positional parameters of Mg(2)SiO(4) as input, structural properties of spinel Zn(2)SiO(4) have also been studied.

Polychlorinated dibenzo-p-dioxin and dibenzofuran levels and patterns in polyvinylchloride and chloralkali industry workers.

The production of chlorine and vinyl chloride (VCM) is associated with the formation of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). The objective of the present study was to determine whether the levels and congener patterns of PCDDs and PCDFs in the blood of workers involved in the production of such substances could be related to their occupational environment. PCDD and PCDF levels in blood plasma from VCM and chloralkali workers and in referents were determined by means of high-resolution gas chromatography/high resolution mass spectrometry (HRGC/HRMS) techniques and the results were evaluated through principal component analysis (PCA). The overall levels of PCDDs and PCDFs were low, but the relative congener distribution detected in the workers differed from that found in the referents. 1,2,3,4,6,7,8-HpCDF, 1,2,3,4,7,8- and 1,2,3,6,7,8-HxCDFs are congeners related to work in VCM and chloralkali industries. Exposure to PCDDs and PCDFs in these industrial environments changes the congener-distribution pattern in the blood of workers as compared with referents. A combination of isomer-specific analysis of PCDDs and PCDFs in blood plasma and PCA is suitable for the differentiation between nonoccupational and occupational exposure and provides a means of assessing workers' exposure situation in different occupational settings.

Biomarkers of exposure, antibodies, and respiratory symptoms in workers heating polyurethane glue.

OBJECTIVES: The pathogenic basis of respiratory disorders associated with isocyanates are still obscure. One reason for this is the lack of good estimates of human exposure. In this study exposure was estimated by measurement of isocyanate metabolites in biological samples. METHODS: In a factory using isocyanate based polyurethane (PUR) glue, isocyanate concentrations in air were measured by liquid chromatography. Samples from 174 employees were analysed for metabolites of 4,4'-methylene diphenyl diisocyanate (MDI) in plasma (P-MDX) and urine (U-MDX). After hydrolysis, 4,4'-methylenedianiline was measured by gas chromatography-mass spectrometry (GC-MS). The employees were screened for work related respiratory symptoms and tested for specific immunoglobulin E (IgE) and IgG antibodies directed against isocyanate conjugated to human serum albumin. RESULTS: The time weighted isocyanate concentrations in air were low (MDI < 0.2-7; hexamethylene diisocyanate (HDI) < 0.1-0.7; 2,6-toluene diisocyanate (TDI) < 0.1 microgram/m3). All subjects had detectable P-MDX and U-MDX. There were significant associations between the estimates of exposure to thermal degradation products of an MDI based glue and P-MDX (range < or = 0.10-5.5 micrograms/l); and U-MDX (< or = 0.04-5.0 micrograms/g creatinine); in cases of heavy exposure. P-MDX and U-MDX were associated with each other (r = 0.64; P = 0.0001), work related symptoms (P-MDX: P = 0.03; Mann-Whitney U test), and serum concentrations of MDI specific IgG antibodies (r = 0.26; P = 0.0007). Unexpectedly, high P-MDX and U-MDX concentrations were also encountered in workers cutting textile (P-MDX 2.4-4.5 micrograms/l; U-MDX 0.81-3.8 micrograms/g creatinine); the reason is still unknown. Equally unexpected, there were significant negative associations between P-MDX and liver function tests. CONCLUSIONS: The results clearly show the value of biomarkers for isocyanate exposure; in particular, P-MDX is useful. Further, these results show the risk connected with thermal degradation of PUR.

Cancer incidence and mortality of patients with suspected solvent-related disorders.

OBJECTIVE: The aim of this study was to study the incidence of cancer and deaths from cancer and other diseases among patients referred to the 11 clinics of occupational medicine in Sweden between 1967 and 1987 for examination because of exposure to organic solvents. METHODS: The cohort comprised 5791 persons, 5283 men and 508 women. Information about cancer incidence and causes of death was collected from the Cancer Register of the National Board of Health and Welfare and the National Death Register of Statistics Sweden, respectively. The expected values were calculated from the national death rates and incidence rates of cancer. RESULTS: The overall mortality rate was close to expected, but the mortality rate was decreased for diseases of the circulatory system [standardized mortality ratio (SMR) 0.7, 95% confidence limit (95% CI) 0.5-0.9] and increased for suicide (SMR 2.0, 95% CI 1.2-3.2). The total cancer incidence was slightly elevated [standardized incidence ratio (SIR) 1.2, 95% CI 0.99-1.4], and some specific cancer sites showed an increased incidence, although the lower confidence limits surpassed one. Malignancies of the lymphohematopoietic system and cancer of the uterine cervix had an increased risk (SIR 1.9, 95% CI 1.2-3.2, and SIR 3.7, 95% CI 2.2-6.2, respectively). Patients with presumerably high solvent exposure had an SIR of 1.4 for all malignancies (95% CI 0.9-2.1) and those with presumerably low exposure had an SIR of 1.1 (95% CI 0.9-1.4). CONCLUSIONS: The study showed an increased risk for malignancies of the hematopoietic system and the uterine cervix among patients originally examined with regard to solvent-induced disorders. There was also an increased risk of suicide and a decreased risk of death from diseases of the circulatory system. There was no increased risk for deaths from mental or neurological disorders.

Mortality and cancer incidence among Swedish fishermen with a high dietary intake of persistent organochlorine compounds.

OBJECTIVES: The objective of this study was to determine mortality and cancer incidence in two cohorts of Swedish fishermen with different dietary intakes of persistent organochlorine compounds. METHODS: The following two cohorts of Swedish fishermen were established: a cohort of 2896 subjects from the Swedish east coast (on the Baltic Sea), and a cohort of 8477 subjects from the Swedish west coast. Mortality and cancer incidence were studied in these cohorts and comparisons were made both with the regional populations and between the cohorts. RESULTS: The incidences of stomach and squamous cell skin cancers among the eastcoast fishermen were elevated as compared with those of the regional population [standardized incidence ratio (SIR 1.6, 95% confidence interval (95% CI) 1.0-2.4 and SIR 2.3, 95% CI 1.5-3.5 respectively] and with the westcoast cohort (IRR 2.2, 95% CI 1.3-3.5 and IRR 1.9, 95% CI 1.2-3.1, respectively), while that of colon cancer was decreased. Moreover, mortality from multiple myelomas was increased among the eastcoast fishermen as compared with that of the general population [standardized mortality ratio (SMR) 3.1, 95% CI 1.2-6.4) and the westcoast fishermen (IRR 3.2, 95% CI 1.2-8.7). A 12% decreased mortality in ischemic heart disease was found for the eastcoast cohort. A slight, but significant increase in such deaths was noted among the westcoast fishermen. CONCLUSIONS: High consumers of fatty fish, contaminated with organochlorine compounds, had an increased risk for stomach and skin cancer. They also had a suggestive decrease in mortality from ischemic heart diseases.

Fish consumption and exposure to persistent organochlorine compounds, mercury, selenium and methylamines among Swedish fishermen.

OBJECTIVES: This study assessed dietary habits and exposure to selenium, persistent organochlorine compounds, methylmercury, and methylamines among Swedish fishermen. METHODS: Two hundred and fifty randomly selected subjects from a cohort of 2896 fishermen from the Swedish east coast (Baltic Sea) and 8477 fishermen from the west coast (Skagerrak and Kattegatt) were interviewed along with 250 referents. Subgroups of fishermen and referents from different coastal areas were also selected for blood and urine sampling. RESULTS: The interview data showed that fishermen ate almost twice as much fish as the 250 referents from the general population. The blood levels of mercury were twice as high, and the plasma selenium levels were 10-15% higher in the fishermen than in the referents. There was, however, no difference between the fishermen's cohorts with respect to these variables. Fishermen from the east coast ate more fatty fish than fishermen from the west coast, and they also had higher blood levels of persistent organochlorine compounds such as polychlorinated biphenyls and polychlorinated dibenzo p-dioxins and furans (present in fatty fish species in the Baltic Sea) than both the westcoast fishermen and the referents. CONCLUSIONS: A cohort of Swedish eastcoast fishermen might be a suitable study base for epidemiologic studies on the mortality and cancer morbidity associated with dietary exposure to persistent organochlorine compounds.

Selenoprotein P and glutathione peroxidase (EC 1.11.1.9) in plasma as indices of selenium status in relation to the intake of fish.

In Sweden fish is considered to be an important source of dietary Se. Therefore Se status was assessed in forty-one middle-aged men with widely varying fish consumption. Glutathione peroxidase (EC 1.11.1.9) and selenoprotein P in plasma were measured by radioimmunoassay. Plasma Se among the men increased slightly with increasing consumption of fish, but no such increases in the concentrations of glutathione peroxidase and selenoprotein P in plasma were observed. Moreover, no correlation was found between plasma Se and glutathione peroxidase or selenoprotein P. Instead, glutathione peroxidase was significantly correlated with selenoprotein P (r 0.73, P < 0.001), indicating that both glutathione peroxidase and selenoprotein P were functional indicators of Se status in this group. The proportion of plasma Se located in glutathione peroxidase decreased with increasing plasma Se. The results suggest that the Se consumed from fish had no apparent effect on the amount of Se incorporated into the functional selenoproteins of plasma. It is concluded that in some cases selenoproteins may be better biological markers of Se status than the total concentration of Se.

Polychlorinated biphenyls, 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (p,p'-DDT) and 1,1-dichloro-2,2-bis(p-chlorophenyl)-ethylene (p,p'-DDE) in human plasma related to fish consumption.

Fatty fish species, e.g., salmon and herring, in the Baltic Sea have high levels of polychlorinated biphenyls (PCBs) and 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (p,p'-DDT), and its main metabolite: 1,1-dichloro-2,2-bis(p-chlorophenyl)-ethylene (p,p'-DDE). We determined levels of 10 different PCB congeners, including non- and mono-ortho-PCBs, as well as DDT and DDE, in human blood plasma from 37 subjects with varying intake of fish (0-1 750 g/wk) from the Baltic Sea. With respect to all of the PCB congeners we investigated, as well as for DDT and DDE, there were statistically significant associations with fish intake. Thus, fish from the Baltic Sea is a major source of exposure to these compounds in Swedes. Polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF) had been determined earlier in 29 of the subjects. The PCB contribution to "dioxin-like" effects among high consumers of fish (calculated as Nordic TCDD equivalents) was almost 80%, whereas that from PCDD and PCDF was only 20%.

Exposure to mixtures and congeners of polychlorinated biphenyls.

There are 209 congeners of polychlorinated biphenyls (PCBs), the metabolism and toxicity of which vary by congeners. Use of PCBs is now restricted, but environmental contamination and human exposure persist. Analysis for "total PCBs" in biological samples gives limited information; congener-specific analysis is far more informative, but more complicated. Concentrations of congeners in serum/plasma, adipose tissue, or milk are useful biomarkers of exposure. Lipids may contain similar concentrations and congener patterns, but these vary between exposures and are different from those of the corresponding exposure mixtures; hence, analysis of lipids cannot be used to identify the original exposure. Some non- and mono-ortho congeners may attain a coplanar conformation, which renders them capable of a dioxin-like action. Toxic equivalency factors (TEFs) have been used to sum that risk as toxic equivalents (TEQs), which are considerably different from congener concentrations. No reliable data have been developed on the relationship between concentrations of "total PCBs" or congeners in biological samples and effects of PCBs on human health, mainly because of the various analytical procedures involved and confounding exposures.

Urinary excretion of methylamines in men with varying intake of fish from the Baltic Sea.

Fish contain methylamines, especially trimethylamine N-oxide (TMAO), trimethylamine (TMA), and dimethylamine (DMA). Further, DMA may be formed TMA and TMAO. DMA is a precursor of nitrosodimethylamine (NDMA), which is a potent carcinogen. Levels of DMA, TMA, and TMAO in urine were used as indicators of the dietary exposure and in vivo formation of these amines in 44 men, representing 3 groups with different fish consumption habits. The levels of TMA (median 0.24 mmol/mol creatinine; range 0-2.7) and TMAO (median 38 mmol/mol creatinine; range 8-290) were significantly associated with the weekly intake of fish (r = .47, p = .001, and r = .53, p = .0002, respectively), while no such relation was found for DMA (median 24 mmol/mol creatinine; range 5-46). Further, urinary levels of TMA and TMAO were dependent on recent intake of fish.

Parameters of immunological competence in subjects with high consumption of fish contaminated with persistent organochlorine compounds.

Consumption of fatty fish species, like salmon and herring, from the Baltic Sea is an important source of human exposure to persistent organochlorine compounds, e.g. polychlorinated dioxins (PCDDs), dibenzofurans (PCDFs) and biphenyls (PCBs). Many of these compounds show immunotoxic and hepatotoxic effects in animals. We have now studied immunological competence, including lymphocyte subsets, in 23 males with a high consumption of fish from the Baltic Sea and in a control group of 20 males with virtually no fish consumption. The high consumers had lower proportions and numbers of natural killer (NK) cells, identified by the CD 56 marker, in peripheral blood than the non-consumers. Weekly intake of fatty fish correlated negatively with proportions of NK cells (rs = -0.32, P = 0.04). There were also, in a subsample of 11 subjects, significant negative correlations between numbers of NK cells and blood levels of a toxic non-ortho-PCB congener (IUPAC 126; rs = -0.68, P = 0.02) and a mono-ortho congener (IUPAC 118; rs = -0.76, P = 0.01). A similar correlation, in 12 subjects, was seen for p,p'-DDT (rs = -0.76, P = 0.01). The corresponding negative correlation, in 13 subjects, with blood levels of PCDD/Fs was not significant (rs = -0.57, P = 0.07). No significant association was seen between organic mercury in erythrocytes and NK cells. Fish consumption was not associated with levels of any other lymphocyte subset. Neither were there any correlations with plasma immunoglobulins or liver enzyme activities. Our study indicates that accumulation of persistent organochlorine compounds in high consumers of fatty fish may adversely affect NK cell levels.