Cytochemical demonstration of mercury deposits in trout liver and kidney following methyl mercury intoxication: differentiation of two mercury pools by selenium

The amount and the ultrastructural distribution of mercury was studied in seven different organs of rainbow trout (Salmo gairdneri) fingerlings following exposure to methyl mercury (MeHg)-contaminated fodder for periods of 2 and 7 weeks. The amounts of mercury retained by the whole fish and the selected organs were determined by measuring the uptake of 203Hg-labeled MeHg. Spleen, liver, and kidney had the highest concentrations after both experimental periods, while the largest relative increases were found in brain, muscle, and kidney. The subcellular distribution of mercury accumulations was demonstrated cytochemically in liver and kidney using the silver enhancement method by which accumulations of mercury-sulfides and/or mercury-selenides are made visible for light and electron microscopy. When sections prepared from the liver and kidney from fish, injected with selenium 2 hr prior to being killed, were compared with those of fish not treated with selenium, two distinct pools of mercury could be demonstrated, the HgS pool, and the HgSe pool. The HgS pool, supposed to represent inorganic mercury, was found exclusively within lysosomes. The increase of this pool from 2 to 7 weeks was most pronounced in the kidney. The HgSe pool, supposed to represent methyl mercury, was shown by the presence of silver deposits at new locations as well as by an increase in the amount of deposits within lysosomes. The new locations included (1) secretory-like vesicles and the bile canaliculi of the liver, suggesting a biliary excretion of this mercury pool; (2) microvilli and endosomes of kidney tubular cells, suggesting a glomerular filtration and subsequent reabsorption; and (3) mitochondria of proximal tubule cells.     

Role of selenium in mercury intoxication in mice

Studies were conducted to examine the effect of pre and post-treatment of selenium in mercury intoxication (20 micromole/ kg b.w. each given intraperitoneally) in mice in terms of lipid peroxidation (LPO), glutathione (GSH) content, activities of superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT) and mercury concentration in liver, kidney and brain. No significant alteration was observed in all the organs examined after mercury or selenium treatment in LPO and GSH but administration of selenium (pre and post) resulted in an increase in the level of LPO and GSH. The activity of SOD was depleted in liver and kidney while that of GPx was lowered in liver of mercury exposed animals. Selenium administration resulted in restoration of the depletion of these enzymatic activities. The activity of CAT in liver and brain was enhanced both in mercury and selenium treated animals. Administration of selenium significantly arrested enhanced CAT activity. Kidney showed the highest mercury concentration among the organs examined. Administration of selenium resulted in further enhancement of mercury concentration in the tissues. An increase in selenium level in liver was observed after mercury treatment, which was also restored by mercury selenium co-administration. Our results indicate that the prooxidant effect of selenium was greater by its pretreatment.     

Generation and dose as modifying factors of inorganic mercury accumulation in brain, liver, and kidneys of rats fed methylmercury

Through three generations, male rats were fed a commercial chow supplemented with four levels of methyl mercury; the average mercury concentrations were 0.038, 0.18, 7.23, and 33.92 nmol Hg/g food for control, low, middle, and high dose groups, respectively. No clinical abnormalities except enlarged kidneys were found in these animals. The effects of dose and generation on tissue distribution and accumulation of inorganic mercury and total mercury were studied in the brain, kidneys, and liver. The dose level of methyl mercury greatly determined the organ accumulation of total mercury and inorganic mercury, as well as the ratio of inorganic mercury concentration to total mercury concentration (I/T) in organs. The I/T ratio was inversely related to the dose level of methyl mercury. With generational procession, the most notable change was found in the liver, i.e., the increasing I/T ratio and the decreasing total mercury accumulation at any dose level. In contrast, the I/T ratio in the kidney showed no constant tendency with generation. The present results suggest that the generational enhancement of inorganic mercury formation from methyl mercury occurs mainly in the liver.     

Factors contributing to the difference of hair mercury concentrations between the sexes

Scalp hair samples were collected by mail from 97 married couples who were living in several places in Okinawa-prefecture and supposedly had no specific exposure to mercury compounds. They were selectively analysed for organic and inorganic mercury content and the difference of hair mercury concentration between the sexes was discussed in relation to the frequency of fish intake, fish species, drinking habits and permanent-wave hair treatment. Results obtained were as follows: 1) The increase in hair levels of organic and inorganic mercury concentrations was roughly proportional to the dietary intake of fish in the range from none or low to moderate frequencies for both husbands and wives. However, this increase was not proportional to the dietary intake of fish in the range from moderate to high frequencies, showing almost the same level irrespective of the frequency of fish intake. 2) Though husbands and wives had dietary consumption patterns quite similar to each other, husbands were found to have higher hair organic mercury levels than wives, the average values being 6.40 ppm with a standard deviation of 4.69 ppm for husbands and 2.86 ppm with a standard deviation of 1.97 ppm for wives, respectively. The difference was statistically significant. No significant difference between the sexes was detected for inorganic mercury concentrations. However, a highly significant positive correlation coefficient for organic mercury and also a significant positive correlation coefficient for inorganic mercury were found between husbands and wives. 3) Hair without permanent-wave treatment showed higher levels of organic mercury concentrations than hair with permanent-wave treatment for both husbands and wives. Drinkers also had higher levels of hair mercury as compared to non-drinkers. However, the lower levels of organic mercury concentrations in women's hair than in men's hair were not fully explained by these factors. 4) Both men and women who showed higher hair levels of organic mercury had a preference for highly predatory fish such as tuna and bonito, which probably contributed most to the human intake of mercury.     

Mercury and Selenium Content in Selected Seafood

The mercury and selenium contents of fresh seafood were determined, respectively, by means of cold vapor atomic absorption spectroscopy (CVAAS) and hydride-generation atomic absorption spectrometry (HGAAS). All the values obtained were lower than the European Union's legal limit of 0.5 mg/kg fresh food, rising to 1.0 mg/kg for the edible parts of some listed species; in fish they vary between 0.057 mg/kg in sole and 0.579 mg/kg in swordfish (included in the category of large fish, for which the legal limit is 1 mg/kg). The levels of selenium vary between 0.073 mg/kg in perch and 0.743 mg/kg in tuna. In shellfish the mercury content varies between 0.023 mg/kg in moscardino and 0.150 mg/kg in Mediterranean shrimp, while that of selenium varies between 0.067 mg/kg in spiny lobster and 0.605 mg/kg in mussels. A significant difference was found between fish and shellfish for mercury, but not for selenium. A large excess of selenium in relation to mercury was observed (the mean molar ratio of Hg/Se is 0.23 for fish and 0.09 for shellfish), but no significant correlation was found between the two elements.     

Histochemical demonstration of two mercury pools in trout tissues: Mercury in kidney and liver after mercuric chloride exposure

Juvenile rainbow trout (Salmo gairdneri) were exposed to 100 ppb mercury (as HgCl2) in the water for 14 days. Concentrations of mercury in water and fish organs were monitored using radiolabeled mercury. Tissues from kidney and liver were fixed, and sections were developed by autometallography, a method whereby accumulations of mercury sulfides and/or mercury selenides are silver amplified. In the kidney, mercury was found within lysosomes and extracellularly in the basal lamina of proximal tubules. In the liver, mercury was found within lysosomes of the hepatocytes. Additional groups of mercury-exposed trout were subjected to selenium (as Na2SeO3), administered intraperitoneally 2 hr before fixation. Following this treatment, additional mercury could be visualized in the kidney circulatory system, including glomeruli, and in the nucleus and endoplasmic reticulum of liver cells. It is suggested that the mercury visualized prior to selenium treatment represents inorganic mercury, while additional mercury visualized after selenium administration represents an organic form.     

Relation of mercury exposure to elemental mercury levels in the urine and blood

The levels of elemental and inorganic mercury were measured in urine and blood samples from workers in thermometer manufacturing factories. The inorganic mercury levels in the urine did not correlate with the levels of mercury exposure for each worker. However, a significant correlation was noted between elemental mercury levels in the urine and the levels of individual exposure. A significant correlation was also found between elemental mercury levels in the urine and mercury levels in the blood. These findings suggest that the determination of elemental mercury in urine may serve as a useful indicator for assessing levels of recent exposure to mercury vapor, as well as the level of inorganic mercury in the blood.     

Risk to consumers from mercury in Pacific cod (Gadus macrocephalus) from the Aleutians: fish age and size effects

While there has been considerable attention devoted to the risks to high level consumers from mercury in freshwater fish, relatively little attention has been devoted to saltwater fish. Although the U.S. Food and Drug Administration has issued advisories based on mercury for four saltwater species or groups of fish, there are few data on mercury levels generally, or on the risk these levels pose to the fish themselves or to consumers of marine fish. We examined total mercury levels in liver and muscle of Pacific cod (Gadus macrocephalus) collected from the northern Pacific and Bering Sea waters around Nikolski, Amchitka, and Kiska Islands in the Aleutian Chain (Alaska). We were interested in whether there were differences in mercury levels as a function of location, weight, length, and age of the fish, and what risk mercury posed to the food chain, including people. Fish were aged by examining otoliths, and we measured selenium because of its reported protective effects against mercury. Regression models indicated that 27% of the variation in levels of mercury was due to tissue examined and age, while 67% of the variation in levels of selenium was due to tissue, length, and age. Mercury levels were significantly higher in the muscle than the liver, and the reverse was true for selenium. Mercury levels were negatively correlated with selenium levels, and positively correlated with length, weight, and age. There were no gender differences in mercury or selenium levels. The mean levels of mercury in muscle (0.17 ppm wet weight) are within the range known to cause adverse effects in sensitive birds and mammals. Only 4% of the Pacific cod samples had mercury levels above 0.5 ppm, the action level promulgated by many states and countries, and none were above the 1 ppm action level of the U.S. FDA.     

Mercury in canned tuna: white versus light and temporal variation

There are abundant data and advisories for mercury levels in wild fish, but far fewer for commercial fish that compose a large majority of the fish most people eat. Until recently, relatively little attention has been devoted to examining mercury in canned tuna, despite its great importance in human diets. There is substantial media coverage of the benefits and risk from fish consumption, but few peer-reviewed data on canned tuna, the most commonly consumed fish in the United States. In this paper, we examine the levels of total mercury in canned tuna obtained from a New Jersey grocery store from 1998 to 2003, looking for temporal consistency within this data set and particularly for comparison with the Food and Drug Administration's 1991 study. We analyzed 168 cans individually for total mercury. All values are reported as parts per million (= microg/g) on a wet weight basis. In a subset of samples analyzed for total and inorganic mercury, the inorganic mercury was below detection levels; hence at least 89% of the mercury can be considered methylmercury. We found that white-style tuna had significantly more total mercury (mean 0.407 ppm) than light-style tuna (mean 0.118 ppm), presumably reflecting that "white" tuna is albacore, a species relatively larger than the skipjack tuna, which is commonly available as "light" or "chunk light." The maximum mercury in a can was 0.997 ppm, but 25% of white tuna samples exceeded 0.5 ppm. Data suggest a slight increase in levels since 1991, and mercury levels were significantly higher in 2001 than in other years. The mean level of mercury in white tuna (mean 0.407 ppm) was significantly higher than the mean value of 0.17 ppm currently used by the U.S. Food and Drug Administration (FDA) in its risk assessment and public information. There were no significant differences in mercury levels in tuna packed in oil compared to water. Draining contents had no effect on mercury levels, and the fluid, both oil and water, contained little mercury. These data indicate that people who eat canned tuna frequently can choose light tuna and reduce their mercury intake. Canned mackerel had much lower levels of mercury than tuna. Since cans of white tuna frequently exceed the FDA's original action level of 0.5 ppm, it would be prudent to continue some systematic monitoring of the nation's canned fish supply, particularly as the targets of commercial fisheries inevitably change as certain stocks become depleted.     

Prenatal exposure to methyl mercury among Greenlandic polar Inuits

During the period 1982 to 1988, 37 paired samples of blood from Inuit women and their newborn children were collected in North Greenland. The samples were analyzed for whole blood content of total mercury (tot-Hg) and for content of methyl mercury (Me-Hg). In maternal blood, 80% of the tot-Hg was found to be methylated in contrast to 98% in cord blood. Concentrations of Me-Hg in maternal and cord blood were significantly correlated, and the mean ratio between fetal and maternal blood Me-Hg was 1.9. Concentrations of Me-Hg in cord blood were closely related to the marine food intake of the mothers. Eighty-four percent of the mothers had blood concentrations of Me-Hg above 0.11 mumol/l (23 micrograms/l), which corresponds to the provisional limit of tolerable intake set by the World Health Organization. This indicates that the majority of the pregnant woman have an unacceptable high intake of methyl mercury.     

Methyl mercury and inorganic mercury in Swedish pregnant women and in cord blood: influence of fish consumption

We studied exposure to methyl mercury (MeHg) in Swedish pregnant women (total mercury [T-Hg] in hair) and their fetuses (MeHg in cord blood) in relation to fish intake. The women were recruited at antenatal care clinics in late pregnancy to participate in an exposure study of environmental pollutants. Fish consumption was evaluated using food frequency questionnaires including detailed questions on fish consumption. In addition, we determined inorganic mercury (I-Hg) and selenium (Se) in cord blood. On average, the women consumed fish (all types) 6.7 times/month (range 0-25 times/month) during the year they became pregnant. They reported less consumption of freshwater fish--species that might contain high concentrations of MeHg--during than before pregnancy. T-Hg in maternal hair (median 0.35 mg/kg; range 0.07-1.5 mg/kg) was significantly associated (R2 = 0.53; p < 0.001) with MeHg in cord blood (median 1.3 microg/L; range 0.10-5.7 microg/L). Both hair T-Hg and cord blood MeHg increased with increasing consumption of seafood (r = 0.41; p < 0.001 and r = 0.46; p < 0.001, respectively). Segmental hair analysis revealed that T-Hg closer to the scalp was lower and more closely correlated with MeHg in cord blood than T-Hg levels in segments corresponding to earlier in pregnancy. We found a weak association between Se (median 86 microg/L; range 43-233 microg/L) and MeHg in cord blood (r = 0.26; p = 0.003), but no association with fish consumption. I-Hg in cord blood (median 0.15 microg/L; range 0.03-0.53 microg/L) increased significantly with increasing number of maternal dental amalgam fillings.     

Effects of coadministered sodium selenite on short-term distribution of methyl mercury in the rat

Adult male Sprague-Dawley rats received iv injections of 1 μmole of methyl mercury/kg alone or coadministered with 5 μmole of sodium selenite/kg. Tissue concentrations of methyl mercury were determined at 5, 20, and 60 min after treatment. Selenite treatment produced a significant increase in cerebral methyl mercury concentrations and a significant decrease in kidney methyl mercury concentrations at all time points. The concentration of methyl mercury in liver was significantly increased by selenite coadministration at 5 and 20 min but at 60 min after injection the concentration was not significantly different from that found in rats receiving methyl mercury alone. Selenite treatment also significantly lowered blood methyl mercury concentrations at all time points. This decrease was associated with a significant decrease in the concentration of methyl mercury in erythrocytes at 5, 20, and 60 min. Plasma methyl mercury levels at 5 min postinjection were slightly higher in selenite-treated rats but were significantly lower in treated animals at 20 and 60 min. Treatment of rats with selenite did not specifically alter the extent of methyl mercury binding to glutathione in the 108,000g supernatant of cerebrum or in erythrocyte hemolysates. In rats receiving either methyl mercury alone or with selenite low-molecular-weight methyl mercury complexes could not be detected in plasma 5 min after iv injection. These results suggested that selenite exerted immediate effects on the distribution of methyl mercury in the rat but did not alter the binding of methyl mercury to glutathione in the soluble components of erythrocytes and cerebrum or lead to formation of a persistent low-molecular-weight methyl mercury complex in plasma.     

Reduced mercury excretion with feces in germfree mice after oral administration of methyl mercury chloride

Summary When methyl mercury chloride was administered orally the amount of mercury excretion with feces of germfree mice was noticeably lower than that of the control mice. Germfree mice excreted 24 percent of the administered mercury within 10 days of administration while the control mice excreted 46 percent. Mercury retention in the organs of germfree mice was slightly higher than in the control mice. These results suggest that the existence of microorganisms in animal intestines are concerned with mercury excretion in the animal body.     

Blood organic mercury and dietary mercury intake: National Health and Nutrition Examination Survey, 1999 and 2000

Blood organic mercury (i.e., methyl mercury) concentrations among 1,709 women who were participants in the National Health and Nutrition Examination Survey (NHANES) in 1999 and 2000 (1999-2000 NHANES) were 0.6 microg/L at the 50th percentile and ranged from concentrations that were nondetectable (5th percentile) to 6.7 microg/L (95th percentile). Blood organic/methyl mercury reflects methyl mercury intake from fish and shellfish as determined from a methyl mercury exposure parameter based on 24-hr dietary recall, 30-day food frequency, and mean concentrations of mercury in the fish/shellfish species reported as consumed (multiple correlation coefficient > 0.5). Blood organic/methyl mercury concentrations were lowest among Mexican Americans and highest among participants who designated themselves in the Other racial/ethnic category, which includes Asians, Native Americans, and Pacific Islanders. Blood organic/methyl mercury concentrations were ~1.5 times higher among women 30-49 years of age than among women 16-29 years of age. Blood mercury (BHg) concentrations were seven times higher among women who reported eating nine or more fish and/or shellfish meals within the past 30 days than among women who reported no fish and/or shellfish consumption in the past 30 days. Blood organic/methyl mercury concentrations greater than or equal to 5.8 microg/L were lowest among Mexican Americans (2.0%) and highest among examinees in the Other racial/ethnic category (21.7%). Based on the distribution of BHg concentrations among the adult female participants in 1999-2000 NHANES and the number of U.S. births in 2000, > 300,000 newborns each year in the United States may have been exposed in utero to methyl mercury concentrations higher than those considered to be without increased risk of adverse neurodevelopmental effects associated with methyl mercury exposure.     

Demethylation and excretion of methyl mercury by the guinea pig

Female guinea pigs were dosed po with 1.0 mg CH₃²⁰³Hg/kg as methylmercuric chloride, 10 times over a 3-week period. Tissue distribution, excretion, and accumulation of inorganic and organic mercury were studied. The highest concentration of mercury was found in the kidney. The greatest decreases of mercury levels were observed in the small bowel, red blood cells, liver, and cerebrum. The half-life of whole body clearance, based on a single compartment model, was 31.6 days. Mercury in the kidney, liver, and cerebrum was bound mainly by nuclear and soluble fractions. The highest ratio of inorganic to total mercury was seen in the kidney, 60% of this being as inorganic mercury. Excretion of mercury in the feces was measured throughout the experiment. The relationship of organic to inorganic mercury was relatively constant at about 1:3. Data on the effects of methyl mercury on tissue concentrations of zinc and copper show that the only change in the copper content was a marked increase in the kidney.     

Blood mercury concentrations following methyl mercury exposure in adult and infant monkeys

Female monkeys (Macaca fascicularis) were dosed chronically with the equivalent of 10, 25, or 50 micrograms/kg/day methyl mercury until at least 90% of estimated blood equilibrium was reached and were then bred to untreated males. Infants were dosed with the same dose their mothers had received. An additional group of infants was dosed with 50 micrograms/kg/day beginning at birth. Infants exposed in utero were born with higher (1.7x) mercury levels than their mothers, but blood mercury levels of the offspring decreased to less than one-half that of the mothers. The steady-state blood levels of the group exposed postnatally were not different from steady-state levels of the group exposed in utero plus postnatally. When dosing was discontinued, the rate coefficient of elimination from blood did not differ between the adults (mothers) and the in utero plus postnatally exposed group, while that of the group exposed postnatally only was lower. There was no indication of a relationship in the rate of elimination for mother-infant pairs. These results suggest that the kinetics of methyl mercury in blood are complicated and may depend on the age of the individual when exposure begins.     

Daily mercury intake in fish-eating populations in the Brazilian Amazon

Although high levels of fish consumption and bioindicators of mercury exposure have been reported for traditional populations in the Amazon, little is known about their actual daily intake of Hg. Using an ecosystem approach, calculate daily mercury intake in adult fish-eaters, examine the relations between mercury intake and bioindicators of exposure and the factors that influence these relations. A cross-sectional dietary survey on fish and fruit consumption frequency was carried out with 256 persons from six villages of the Tapajós River. Fish portion per meal was determined. Mercury concentration was determined for 1123 local fish specimens. Daily mercury intake (microg/kg/day) was determined for men and women from each village using the average fish-mercury concentration for the fish caught in their fishing zone, the average quantity of fish per meal, fish-species frequency consumption and participants' body weight. Fish-mercury averaged 0.33 microg/g+/-0.33. Daily mercury intake varied between 0 and 11.8 microg/kg/day (mean 0.92 microg/kg/day+/-0.89) and varied by gender and village. Mean blood- and hair-mercury were 58.7+/-36.1 microg/l and 17.9+/-11.5 microg/g, respectively. There was a strong and positive relation between blood-mercury and daily mercury intake, with an inverse relation for fruit intake and schooling; significant variations were observed with immigrant status, and among villages. Hair-mercury was directly associated with daily mercury intake and inversely related to schooling and fruit consumption. Fruit consumption modified the relation between daily mercury intake and blood-mercury levels: for the same daily mercury intake, persons eating more fruit had lower blood-mercury concentrations (ANCOVA Interaction term: F=10.9, P<0.0001). The median difference of the ratio of blood-mercury to daily mercury intake between low and high fruit consumers was 26, representing a 26.3% reduction. These findings reveal high levels of daily mercury intake. Rigorous studies for developing risk-based reference doses in the Amazon should be undertaken to orient viable risk-management strategies to reduce exposure, while maintaining fish diet.     

Seafood intake,polyunsaturated fatty acids,blood mercury,and serum C-reactive protein in US National Health and Nutrition Examination Survey (2005–2006)

We examined the association between seafood consumption, mercury concentration, polyunsaturated fatty acids, selenium, and Vitamin D in relation to C-reactive protein using the cross-sectional US National Health and Nutrition Examination Survey 2005–2006. We hypothesized that seafood consumption and fatty acids will be negatively associated, and mercury will be positively associated with C-reactive protein, and that statistical adjustment for these factors will alleviate confounding thereby making these associations more apparent. The study sample included 1217 participants (706 males, 511 females) aged 16–49. Sex-stratified sample weighted multiple linear regression models revealed no associations of mercury, polyunsaturated fatty acids, fish intake, selenium, or vitamin D with serum C-reactive protein. However, when all variables were included together in one model, fish intake was associated with lower levels of CRP in females suggesting confounding in models that do not mutually adjust for seafood contaminants and nutrients. Prospective studies are needed to confirm these findings.     

Bioavailability to rats of selenium in various tuna and wheat products

Bioavailability of selenium (Se) in tuna and wheat at various stages of processing was studied in rats. The protein source of the rat diets was torula yeast with Se supplied by either raw, precooked or canned tuna, or whole wheat flour, whole wheat bread or bran. Sodium selenite was used as the standard. Each Se source was fed at three levels: 0.05, 0.10 and 0.15 ppm. By using increase in glutathione peroxidase (GSH-Px) activity in liver, kidney and whole blood as an indicator of bioavailability, no differences were found among the three tuna products or among the three wheat products tested. However, significantly lower GSH-Px activity was found in the combined tuna groups as compared to the combined wheat groups, suggesting that selenium in wheat was more available than that in tuna. There was a significant increase in the liver Se content of rats fed all levels of Se in canned tuna and in kidney, blood and muscle Se of rats fed 0.10 and 0.15 ppm Se in canned tuna in comparison to the tissue Se content in rats fed these same levels of Se in raw or precooked tuna. Since this did not correspond with an increase in GSH-Px activity it was concluded that it did not represent increased bioavailability of canned tuna. Thus, food processing does not appear to affect Se availability, but Se appears to be more available in wheat than tuna.     

Impact of maternal seafood diet on fetal exposure to mercury, selenium, and lead.

Umbilical cord blood from 1,023 consecutive births in the Faroe Islands showed a median blood-mercury concentration of 121 nmol/l (24.2 micrograms/l); 250 of those samples (25.1%) had blood-mercury concentrations that exceeded 200 nmol/l (40 micrograms/l). Maternal hair mercury concentrations showed a median of 22.5 nmol/g (4.5 micrograms/g), and 130 samples (12.7%) contained concentrations that exceeded 50 nmol/g (10 micrograms/g). Frequent ingestion of whale meat dinners during pregnancy and, to a much lesser degree, frequent consumption of fish, and increased parity or age were associated with high mercury concentrations in cord blood and hair. Blood-mercury levels were slightly lower if the mother had occasionally ingested alcoholic beverages. Mercury in blood correlated moderately with blood selenium (median, 1.40 mumol/l). Increased selenium concentrations were associated with intake of whale meat, alcohol abstention, delivery after term, and high parity. Lead in cord blood was low (median, 82 nmol/l), particularly if the mothers had frequently had fish for dinner and had abstained from smoking.