OBJECTIVES: The effects of occupational and leisure-time exposures on the risk of acute myeloid leukemia (AML) were investigated with emphasis on clonal chromosome aberrations (CCA) and morphological subtypes. METHODS: Consecutively diagnosed cases of AML (N=333) and 1 population referent per case were retrospectively included in the study. Information on worktasks, companies, and leisure-time activities was obtained with telephone interviews. Exposure probability and intensity were assessed by occupational hygienists. Associations were evaluated with logistic regression. RESULTS: Exposure to organic solvents was associated with an increased risk of AML [low exposure: OR 1.5 (95% confidence interval (95% CI) 1.0-2.3, moderate-high exposure: OR 2.3 (95% CI 1.0-5.0)]. For exposure to solvents, but not to benzene, the OR was 1.2 (95% CI 0.69-2.0) for "low" and 2.7 (95% CI 1.0-7.3) for "moderate-high" exposure. The observed effects increased with intensity and duration of exposure. The estimated effects were higher for patients >60 years of age at the time of diagnosis. The effect of exposure to organic solvents was not differential with regard to morphology [except possibly erythroleukemia: OR 4.2, 95% CI 1.0-17 or the presence of CCA in general]. No increased risk for AML with complex CCA or with total or partial losses of chromosomes 5 or 7 were observed, but a higher risk was found for AML with trisomy 8 (OR 11, 95% CI 2.7-42) as the sole aberration. CONCLUSIONS: Exposure to organic solvents was associated with an increased risk of AML. This association was not due to benzene exposure alone and may be modified by age. Furthermore, specific associations with trisomy 8, and possibly also erythroleukemia, were suggested.
The present study aimed to assess the role of fish consumption for the body burden of polychlorinated biphenyls (PCBs) in mothers living in the Aland and Turku archipelago in Finland. The overall objective was to investigate whether there exists an appropriate population for a full-scale prospective study on PCB-related developmental effects in infants. Concentrations of the four major PCBs were determined in whole venous blood and cord blood from 30 delivering mothers, of which 20 subjects consumed fatty fish from the Baltic Sea (2.5-12.5 meals per month) and the remaining 10 mothers did not. The concentrations of CB-118, CB-138, CB-153, and CB-180 in cord blood were generally two- to threefold lower than in whole blood from the mothers, but strong correlations were observed between PCBs in the two matrices (r = .67-.80). Neither the venous blood nor cord blood concentrations of PCBs, however, were correlated with stated fish intake. Moreover, the concentration of CB-153 in plasma was only weakly associated with fish intake, and the level of organic mercury in erythrocytes was not correlated with fish intake at all. The present results of CB-153 concentrations in women's blood are lower than those reported in other recent investigations. A reasonable contributing explanation is the rapid decline during the last decades of PCB in Baltic Sea fish, which has resulted in less impact of fish intake on the body burdens of PCB in relatively young women (median 30 yr in the present study) as compared with older females. The relatively low PCB levels in blood taken together with the low number of yearly deliveries in the archipelago population makes it an inappropriate study base for a prospective study of PCB-related health effects in infants.
OBJECTIVES: To investigate whether application of insulation wool adversely affects lung volumes and increases the occurrence of symptoms of airway irritation. METHODS: Data from nationwide health check ups in 1981-93 of male construction workers born in 1955 or later were used to investigate cross sectional (n = 96,004) and longitudinal (n = 26,298) associations between lung volumes, vital capacity (VC), and forced expiratory volume in one second (FEV1) and exposure to insulation wool by combining a job exposure matrix (JEM) and self reported exposure. Data on 12 month prevalence of persistent cough not associated with the common cold was available for the period 1989-92. Potential confounding from smoking, exposure to asbestos, silica, and isocyanates, was considered in the analyses. RESULTS: For those in the highest exposure category (self reported duration of exposure of > or = 11 years, and high exposure according to the JEM) VC was on average 2.5 cl lower (95% CI -6.5 to 1.5) than in those with no exposure. The corresponding figures for FEV1 was -2.4 cl (95% CI -6.1 to 1.3). In the longitudinal analyses, the yearly change in VC between the first and last spirometry for those in the highest exposure category was 0.50 cl (95% CI -0.97 to 1.98) less than in the unexposed category. The corresponding figure for FEV1 was 0.89 cl (95% CI - 0.70 to 2.06). High exposure to insulation wool, asbestos, or silica, during the 12 months preceding the check up was associated with increased odds ratios (ORs) for persistent cough of the same magnitude as current smoking. CONCLUSIONS: The results indicate no effects on VC or FEV1 from exposure to insulation wool. Recent exposure to insulation wool, asbestos, and silica was associated with an increased prevalence of persistent cough.
This study assessed the health effects of occupational acrylamide exposure using hemoglobin (Hb) adducts as biomarkers of internal dose.
Two hundred and ten tunnel workers exposed for about 2 months to a chemical-grouting agent containing acrylamide and N-methylolacrylamide underwent a health examination. Blood samples were drawn for the analysis of Hb adducts of acrylamide. Fifty workers claiming recently developed or deteriorated symptoms of the peripheral nervous system (PNS) were referred to a neurophysiological examination. Workers with Hb-adduct levels exceeding 0.3 nmol/g globin attended follow-up examinations 6, 12, and 18 months after exposure cessation.
Forty-seven workers had Hb-adduct levels within the normal background range (0.02-0.07 nmol/g globin), while the remaining 163 had increased levels up to a maximum of 17.7 nmol/g globin. Clear-cut dose-response associations were found between the Hb-adduct levels and PNS symptoms. Thirty-nine percent of those with Hb-adduct levels exceeding 1 nmol/g globin experienced tingling or numbness in their hands or feet. A no-observed adverse effect level of 0.51 nmol/g globin was estimated for numbness or tingling in the feet or legs. For 23 workers there was strong evidence of PNS impairment due to occupational exposure to acrylamide. All but two had recovered 18 months after the cessation of exposure.
Occupational exposure to a grouting agent containing acrylamide resulted in PNS symptoms and signs. The use of Hb adducts of acrylamide as a biomarker of internal dose revealed strong dose-response associations. The PNS symptoms were, however, generally mild, and in almost all cases they were reversible.
Comment In: Scand J Work Environ Health. 2001 Aug;27(4):217-811560334
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.
Comment In: Scand J Work Environ Health. 1995 Apr;21(2):81-37618062
OBJECTIVES: A cluster of cancers at one plant in a pharmaceutical company in Sweden was the initiator for this work, which describes the cancer incidence among the laboratory and production workers at this company. METHODS: The investigation is a retrospective cohort study. All employees with possible exposure to chemical, pharmacological, or biological agents and employment for at least six months at the company during 1960-1990 were included. Standardized incidence ratios (SIR) were calculated with the local county population as reference. RESULTS: The total cancer incidence was close to the expected. In a subcohort consisting of the highest exposed employees, an SIR of 3.5 [95% confidence interval (95% CI) 1.5-6.8] was found for urothelial tumors, while there were no urothelial tumors among the workers with the lowest exposure. An evaluation of the exposures among the subjects with urothelial tumors revealed no association with specific exposures in the workplaces. There was also a statistically significant increase in the risk for acute leukemia (SIR 4.5, 95% CI 1.2-12 ). With a 10-year induction-latency period in the calculations, the elevated risk was smaller and not significant. Although the numbers were small, there were also statistically significant overrisks for cancer of the peritoneum, the lip, and the pleura. CONCLUSIONS: A significant increase in the risk for urothelial tumors was found among pharmaceutical workers. All but one of those with urothelial tumors were smokers, but confounding from smoking could probably not explain the risk increase.
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.
Cytogenetic assays in peripheral blood lymphocytes (PBL) have been used extensively to survey the exposure of humans to genotoxic agents. The conceptual basis for this has been the hypothesis that the extent of genetic damage in PBL reflects critical events for carcinogenic processes in target tissues. Until now, no follow-up studies have been performed to assess the predictive value of these methods for subsequent cancer risk. In an ongoing Nordic cohort study of cancer incidence, 3182 subjects were examined between 1970 and 1988 for chromosomal aberrations (CA), sister chromatid exchange or micronuclei in PBL. In order to standardize for the interlaboratory variation, the results were trichotomized for each laboratory into three strata: low (1-33 percentile), medium (34-66 percentile), or high (67-100 percentile). In this second follow-up, a total of 85 cancers were diagnosed during the observation period (1970-1991). There was no significant trend in the standardized incidence ratio with the frequencies of sister chromatid exchange or micronuclei, but the data for these parameters are still too limited to allow firm conclusions. There was a statistically significant linear trend (P = 0.0009) in CA strata with regard to subsequent cancer risk. The point estimates of the standardized incidence ratio in the three CA strata were 0.9, 0.7, and 2.1, respectively. Thus, an increased level of chromosome breakage appears to be a relevant biomarker of future cancer risk.
OBJECTIVES: The purpose of this study was to assess cancer incidence and cardiovascular mortality among women with a high dietary intake of fatty fish from the Baltic Sea (on the Swedish east coast), contaminated with persistent organochlorine compounds. MATERIAL AND METHODS: Cohorts of fishermen's wives from the Swedish east (1989 subjects) and west (6605 subjects) coasts were established. The mortality and cancer incidence were studied in these cohorts, and comparisons were made with respective regional populations and between the cohorts. Dietary interviews were made with 200 randomly selected cohort women and equally many women from the general population. The interviewed east- and westcoast cohort women ate locally caught fatty fish at least twice as often as their referents. RESULTS: Compared with that of the regional population, the breast cancer incidence was higher than expected in the eastcoast cohort [standardized incidence ratio (SIR) 1.29, 95% confidence interval (95% CI) 0.96-1.71], whereas it was lower in the westcoast cohort (SIR 0.89; 95% CI 0.77-1.04). When a direct comparison was made between the two cohorts, the eastcoast women displayed an increased breast cancer incidence (incidence rate ratio 1.35, 95% CI 0.98-1.86). No obvious difference was seen between the two cohorts concerning cardiovascular mortality. CONCLUSIONS: The results support, but do not prove, the hypothesis of an association between exposure to a mixture of persistent organochlorine compounds through fish consumption and an increased risk for breast cancer.
We examined the influence of widely varied consumption of fatty fish from the Baltic Sea and of age on plasma concentrations of polychlorinated biphenyls (PCBs), polychlorobiphenylols (OH-PCBs), 2, 2-bis(4-chlorophenyl)-1,1,1-trichloroethane (4,4'-DDT), 2, 2-bis(4-chlorophenyl)-1,1-dichloroethane (4,4'-DDE), 2,2',4, 4'-tetrabromodiphenyl ether (BDE-47), hexachlorobenzene (HCB), and pentachlorophenol (PCP) in Latvian and Swedish men. Both age and fish consumption were significantly correlated with the concentrations of [sigman]PCB, [sigman]OH-PCB, 4,4'-DDE, 4,4'-DDT, and HCB. In the case of BDE-47, no significant relationship with age was observed, and fish consumption had the largest relative effect on plasma concentrations of this contaminant. This relationship may be a result of exposure to BDE-47 having been more recent than that of PCBs and DDE, or because the half-life of BDE-47 may be shorter than that of PCB and DDE. Latvian men demonstrated higher plasma levels of DDE and DDT but lower levels of [sigman]PCB and PCP than did Swedish men. The corresponding levels of HCB and BDE-47 were similar in both countries. The Spearman's rank correlation coefficient obtained by comparing the level of the metabolite 4-hydroxy-2,3,3',4',5-pentachlorobiphenyl (4-OH-CB107) to the combined levels of its parent compounds, 2,3,3',4, 4'-pentachlorobiphenyl (CB-105) and 2,3',4,4',5-pentachlorobiphenyl (CB-118), was higher than the median correlation coefficient obtained upon comparing the level of this metabolite to all other possible combinations of two PCB levels. No other increased correlation between metabolite and parent PCB concentration was observed.
Exposure to, and the potential effects of, pesticides and persistent organic pollutants in the East Baltic region are reviewed. Exposure of the average population to chlorinated compounds seems lower than in most of western Europe, and current pesticide use is very low. However, due to infrastructure failures and poor management controls, industrial hot spots and inadequate storage sites exist that cause high risks to small population fractions. The low exposure of the general population is indicated by low concentrations of polychlorinated dibenzo-p-dioxins, dibenzofurans and biphenyls in milk fat. Chlorophenol concentrations are also generally lower than in Scandinavia. Some organic pesticides have been found at higher concentrations in Baltic countries and the St. Petersburg area than in Norway, but the range is roughly similar to that in central Europe. Thus the overall risk caused by pesticide residues and persistent organic compounds in the Baltic countries and northwestern Russia is low, but local sites of concern exist.
There is a concern that persistent organohalogen toxicants, such as polychlorinated biphenyls (PCBs), might display endocrine-disrupting effects in exposed populations. In this study the correlations between PCBs and thyrotropin (TSH) and thyroid hormone concentrations in plasma were assessed in adult women.
The study group consisted of 182 fishermen's wives from the Swedish east coast, with a median age of 42 years (range 23-62) and a median current consumption of contaminated fatty fish from the Baltic Sea of two meals per month (range 0-12). TSH, free (FT3) and total (TT3) triiodothyronine and free (FT4) and total (TT4) thyroxin in plasma were analyzed by immunofluorometric assays, and 2,2',4,4',5,5'-hexachlorobiphenyl (CB-153) in plasma was analyzed by gas chromatography with electron capture detection. Twenty other PCB and two hydroxy-PCB congeners were analyzed in subgroups of the women. Plasma lipid analyses were performed with enzymatic techniques.
The CB-153 concentration in plasma (range 16-776 ng/g lipid) was negatively correlated with the TT3 concentrations (range 1.0-3.0 nmol/l, rs = -0.29, P
A 25% lower cancer mortality was found for 1360 Swedish fishermen who fished on the Baltic Sea than for the general population. The fishermen consumed twice as much fish as the population in the same county. In spite of the low overall cancer mortality, increased mortality from myeloma, as well as increased incidences of gastric carcinoma and squamous cell cancer of the skin and lips, was observed in the cohort. The decrease in risk for ischemic heart disease was not significant. Whether the dietary intake of fatty acids and selenium from fish contributed to the decreased risk was difficult to evaluate. Moreover, whether the consumption of fish from the Baltic Sea, contaminated with, for example, polychlorinated dioxins and dibenzofurans and other persistent organochlorine substances, contributed to the observed increased specific cancer risks is not known. However, the net health effect of high fish consumption from the Baltic Sea seems to be positive.
OBJECTIVES: Potroom workers in aluminum reduction plants have increased risks for bladder and lung cancer due to exposure from polycyclic aromatic hydrocarbons (PAH). In this study correlations between measures of the external, internal, and biological effective dose have been studied for PAH. METHODS: Venous blood samples were obtained from 98 male potroom workers and 55 unexposed male blue-collar workers, for the analysis of aromatic adducts to DNA (deoxyribonucleic acid) in lymphocytes, using the 32P-postlabeling technique. 1-Hydroxypyrene in urine was analyzed with high-pressure liquid chromatography. Personal sampling of both particulate and gas phase PAH was performed during a full workday for the potroom workers and for 5 referents. Individual PAH congeners were determined with liquid chromatographic-mass spectrometric and gas chromatographic-mass spectrometric techniques. RESULTS: The respiratory-zone airborne level of the sum of 22 particulate (median 13.2 micro/m3) and the 7 gas phase PAH-congeners (median 16.3 microg/m3) among the potroom workers was a hundred times higher than among the referents. The urinary concentration of 1-hydroxypyrene before work was 30 times higher for the potroom workers (median 3.43 micromol/mol creatinine) than for the referents. Most airborne PAH congeners correlated with the excretion of 1-hydroxypyrene in urine. The frequency of aromatic DNA adducts did not, however, differ between the potroom workers and the referents, and no correlation was found for 1-hydroxypyrene in urine. CONCLUSIONS: Despite an obvious occupational exposure to PAH, no increase in aromatic DNA adducts in lymphocytes was found among the potroom workers.
It has not previously been clear whether cytogenetic biomarkers in healthy subjects will predict cancer. Earlier analyses of a Nordic and an Italian cohort indicated predictivity for chromosomal aberrations (CAS) but not for sister chromatid exchanges (SCES). A pooled analysis of the updated cohorts, forming a joint study base of 5271 subjects, will now be performed, allowing a more solid evaluation. The importance of potential effect modifiers, such as gender, age at testing, and time since testing, will be evaluated using Poisson regression models. Two other potential effect modifiers, occupational exposures and smoking, will be assessed in a case-referent study within the study base.
Chromosomal aberrations (CAs), sister chromatid exchanges (SCEs), and micronuclei (MN) in peripheral blood lymphocytes have for decades been used as cytogenetic biomarkers to survey genotoxic risks in the work environment. The conceptual basis for this application has been the idea that increased cytogenetic damage reflects an enhanced cancer risk. Nordic and Italian cohorts have been established to evaluate this hypothesis, and analyses presented previously have shown a positive trend between CA frequency and increased cancer risk. We now report on a pooled analysis of updated data for 3541 subjects examined for CAs, 2703 for SCEs, and 1496 for MN. To standardize for interlaboratory variation, the results for the various cytogenetic end points were trichotomized on the basis of the absolute value distribution within each laboratory as "low" (1-33 percentile), "medium" (34-66 percentile), or "high" (67-100 percentile). In the Nordic cohort, there was an elevated standardized incidence ratio (SMR) for all cancer among subjects with high CA frequency [1.53; 95% confidence interval (CI), 1.13-2.05] but not for those with medium or low CA frequency. In the Italian cohort, a SMR in cancer of 2.01 (95% CI, 1.35-2.89) was obtained for those with a high CA frequency level, whereas the SMRs for those with medium or low did not noticeably differ from unity. Cox's proportional hazards models gave no evidence that the effect of CAs on total cancer incidence/mortality was modified by gender, age at test, or time since test. No association was seen between the SCEs or the MN frequencies and subsequent cancer incidence/mortality. The present study further supports our previous observation on the cancer predictivity of the CA biomarker, which seems to be independent of age at test, gender, and time since test. The risk patterns were similar within each national cohort. This result suggests that the frequency of CAs in peripheral blood lymphocytes is a relevant biomarker for cancer risk in humans, reflecting either early biological effects of genotoxic carcinogens or individual cancer susceptibility.
The cytogenetic endpoints in peripheral blood lymphocytes: chromosomal aberrations (CA), sister chromatid exchange (SCE) and micronuclei (MN) are established biomarkers of exposure for mutagens or carcinogens in the work environment. However, it is not clear whether these biomarkers also may serve as biomarkers for genotoxic effects which will result in an enhanced cancer risk. In order to assess this problem, Nordic and Italian cohorts were established, and preliminary results from these two studies indicated a predictive value of CA frequency for cancer risk, whereas no such associations were observed for SCE or MN. A collaborative study between the Nordic and Italian research groups, will enable a more thorough evaluation of the cancer predictivity of the cytogenetic endpoints. We here report on the establishment of a joint data base comprising 5271 subjects, examined 1965-1988 for at least one cytogenetic biomarker. Totally, 3540 subjects had been examined for CA, 2702 for SCE and 1496 for MN. These cohorts have been followed-up with respect to subsequent cancer mortality or cancer incidence, and the expected values have been calculated from rates derived from the general populations in each country. Stratified cohort analyses will be performed with respect to the levels of the cytogenetic biomarkers. The importance of potential effect modifiers such as gender, age at test, and time since test, will be evaluated using Poisson regression models. The remaining two potential effect modifiers, occupational exposures and smoking, will be assessed in a case-referent study within the study base.
OBJECTIVES--The purpose of the study was to assess reproductive outcomes, especially birthweight, and the consumption of fatty fish from the Baltic Sea, contaminated with persistent organochlorine compounds, among women from the Swedish east coast. MATERIAL AND METHODS--Cohorts of fishermen's wives from the Swedish east and west coasts were established and linked to the Swedish Medical Birth Register for 1973-1991; 1501 children were born in the eastcoast cohort and 3553 in the westcoast cohort. Comparisons were made with regional populations and between the cohorts. Dietary interviews were made with 69 randomly selected women from the cohorts and 69 referents. RESULTS--The women interviewed from the east- and westcoast cohorts ate locally caught fish more than twice as often as their referents. Compared with the regional population, the women in the eastcoast cohort gave birth to an increased number of infants with low birthweights (
OBJECTIVES: The purpose of this study was to determine the mortality and cancer incidence of long-term lead smelter workers at a primary smelter. METHODS: A cohort of 3979 workers employed for at least 1 year during 1928-1979 and a subcohort of 1992 workers employed in lead-exposed departments (lead only workers) was formed. The expected mortality in 1955-1987 and cancer incidence in 1958-1987 were calculated relative to the county rates, specified for cause, gender, 5-year age groups, and calendar year. A cumulative blood-lead index was used for the dose-response analyses. RESULTS: The lung cancer incidence of the total cohort [standardized incidence ratio (SIR) 2.8, 95% confidence interval (95% CI) 2.1-3.8] and the group with the highest exposure (SIR 3.1, 95% CI 2.0-4.6) was high. Similar risk estimates were observed with a latency of 15 years. The workers hired before 1950 had higher lung cancer risk estimates (SIR 3.6, 95% CI 2.6-5.0) than the workers hired later (SIR 1.3, 95% CI 0.6-2.6, no latency period). The risk estimates for lung cancer were further elevated in the subcohort of lead-only workers (SIR 5.1, 95% CI 2.0-10.5 in the highest exposed subgroup; latency period of 15 years). No excesses of other malignancies were noted. CONCLUSIONS: The increased relative risks were probably mainly due to interactions between lead and other carcinogenic exposures, including arsenic. Further study is required concerning such possible interactions before a role in the induction of lung cancer can be ascribed to lead.
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.