José G. Dórea

PERSISTENT, BIOACCUMULATIVE AND TOXIC SUBSTANCES IN FISH: HUMAN HEALTH CONSIDERATIONS

Fish are important dietary items that provide essential nutrients. Fish however, bioaccumulate monomethyl mercury (MMHg) and organo-halogenated pollutants (OHP) that are persistent bioaccumulative and toxic substances (PBTS). Unlike man-made OHP, MMHg is mainly of natural origin but background concentrations of aquatic systems are determined by the environmental Hg-methylating potential. Industrial activities can modulate environmental discharges and fish bioaccumulation of PBTS. Fish and seafood consumption are associated with human body load of PBTS, but farming practices that utilize fishmeal increase the terrestrial food chain resulting in farm-animal accumulation of PBTS. These substances are neurotoxic and endocrine active that can impact humans and wild life, but chemical characteristics of MMHg and OHP modulate interactions with animal tissues. MMHg is protein reactive with a faster metabolism (months) than OHP that are stored and slowly (years) metabolized in fat tissues. Except for brain-Hg, neither Hg nor OHP in tissues are markers of toxic effects; however, deficits in neurobehavioral test-scores of children have been shown in some fish-eating populations. These deficits are transient and within normal range, and are not prodromes of neurological diseases. Although population studies show that consumption of fish at current levels of contamination do not explain neurological disorders, endocrine activity remains controversial. Understanding risk of hazard caused by fish-PBTS consumption requires a wide range of expertise. We discuss chemical, toxic, metabolic, and ecological characteristics associated with PBTS in fish. There are proven health outcome derived from fish consumption, while risk of exposure to avoidable PBTS is a chance that can be minimized by societal actions.

Iodine nutrition and breast feeding.

A survey of the databanks Medline and Web of science identified studies dealing with maternal and infant iodine nutrition during breast feeding. The iodine concentration of human milk varies widely due to maternal iodine intake. Mean breast milk iodine concentrations are reported as ranging from 5.4 to 2170 microg/L (median 62 microg/L) in worldwide studies. In the few studies that compared length of lactation, gestation length, and parity number, these factors did not significantly affect milk-iodine concentrations. In studies of maternal iodine deficiency, untreated goiter had no impact on breast milk iodine when compared with controls. Iodine in human milk responds quickly to dietary iodine intake, either supplemented or consumed in natural foods. Easily absorbable iodine from foods, supplemental sources, iodine-based medication or iodine-based antiseptic solutions used during parturition, is taken up by the maternal thyroid and mammary glands through the Na(+)/I(-) symporter system. This transmembrane carrier protein transports iodine against a high concentration gradient. Hormonal iodine in breast milk occurs mainly as T-4, but depending on maternal iodine intake, high concentrations of the inorganic form (iodide) are found. In less developed countries, where natural-food-iodine intake is low, adequate maternal iodine nutritional status depends exclusively on enforcement of food iodination. In industrialized countries, maternal iodine intake has increased as a function of increasing consumption of dairy products. The human infant is sensitive to maternal iodine nutrition during fetal development and later during breast feeding. Environmental factors, not directly related to maternal iodine intake, such as intake of selenium and organochlorine pollutants, can affect thyroid hormone homeostasis in breast-fed infants. In spite of low iodine concentrations found in milk of mothers consuming low-iodine natural foods, long lasting or even life-lasting benefits to the breast-fed infant are demonstrable.

Iron and copper in human milk.

The reported concentrations of iron and copper in breast milk show a wide variation. Research published over the past 50 y has reported median values of 0.47 and 0.32 mg/L for iron and copper, respectively. The levels of both metals decrease with the progress of lactation. The calculated iron-to-copper ratio of reported means differs from 0.25 to 6.29 (median = 1.18). Maternal constitutional variables such as undernutrition, iron and copper body reserves, stage of lactation, adolescent motherhood, gestation length, and infection and environmental variables such as iron and copper dietary intake, in addition to supplementation, smoking, vegetarianism, and prolonged use of hormonal contraceptives before and during lactation did not consistently affect the concentrations of iron and copper in breast milk. Extreme cases of either low or high levels of body metal availability or altered metabolism due to chelating therapy or illnesses such as Wilsons disease and infections did not affect metal transfer from blood serum to breast milk. There is no clinical or scientific support for the need of extra iron or copper, besides the quantities provided by milk in the full-term breast-fed infant, at least during the first 6 mo.

Fish are central in the diet of Amazonian riparians: should we worry about their mercury concentrations?

The Amazon rain forest extends over an area of 7.8x10(6)km(2) in nine countries. It harbors a diverse human population distributed in dense cities and isolated communities with extreme levels of infrastructure. Amazonian forest people, either autochthons or frontier riparians (ribeirinhos) living in isolated areas, share the same environment for survival and nutritional status. The peculiarities of the hydrological cycle determine disease patterns, agricultural conditions, and food availability. Feeding strategies depend heavily on cassava products and fish. These two foods carry toxic substances such as linamarin (naturally present in cassava) and monomethyl mercury (MMHg) (bioconcentrated in fish flesh) that cause neurotoxic diseases in other parts of the world but not in Amazonia, where neurotoxic cases of food origin are rare and not related to these staples. While cassava detoxification processes may partly explain its safe consumption, the Hg concentrations in Amazonian fish are within traditionally safe limits for this population and contribute to an important metabolic interaction with cassava. The gold rush of the 1970s and 1980s brought large-scale environmental disruption and physical destruction of ecosystems at impact points, along with a heavy discharge of metallic Hg. The discharged Hg has not yet impacted on MMHg concentrations in fish or in hair of fish consumers. Hair Hg concentration, used as a biomarker of fish consumption, indicates that the Amazonian riparians are acquiring an excellent source of protein carrying important nutrients, the lack of which could aggravate their existing health problems. Therefore, in a scenario of insufficient health services and an unhealthy environment, food habits based on fish consumption are part of a successful survival strategy and recommendations for changes are not yet justifiable.

Toxicity of ethylmercury (and Thimerosal): a comparison with methylmercury

Ethylmercury (etHg) is derived from the metabolism of thimerosal (o‐carboxyphenyl‐thio‐ethyl‐sodium salt), which is the most widely used form of organic mercury. Because of its application as a vaccine preservative, almost every human and animal (domestic and farmed) that has been immunized with thimerosal‐containing vaccines has been exposed to etHg. Although methylmercury (meHg) is considered a hazardous substance that is to be avoided even at small levels when consumed in foods such as seafood and rice (in Asia), the World Health Organization considers small doses of thimerosal safe regardless of multiple/repetitive exposures to vaccines that are predominantly taken during pregnancy or infancy. We have reviewed in vitro and in vivo studies that compare the toxicological parameters among etHg and other forms of mercury (predominantly meHg) to assess their relative toxicities and potential to cause cumulative insults. In vitro studies comparing etHg with meHg demonstrate equivalent measured outcomes for cardiovascular, neural and immune cells. However, under in vivo conditions, evidence indicates a distinct toxicokinetic profile between meHg and etHg, favoring a shorter blood half‐life, attendant compartment distribution and the elimination of etHg compared with meHg. EtHgs toxicity profile is different from that of meHg, leading to different exposure and toxicity risks. Therefore, in real‐life scenarios, a simultaneous exposure to both etHg and meHg might result in enhanced neurotoxic effects in developing mammals. However, our knowledge on this subject is still incomplete, and studies are required to address the predictability of the additive or synergic toxicological effects of etHg and meHg (or other neurotoxicants). Copyright

Indices of mercury contamination during breast feeding in the Amazon Basin

Mercury pollution, due to gold mining has spread through the Amazon ecosystem reaching the food chain and affecting the indigenous people of the region. We studied the mercury contamination of 47 mothers and infants and the role of breast feeding in indices of mercury body burden in both groups, by measuring hair and milk Hg levels. Total mercury concentration of breast milk ranged from 0.0 to 24.8 (5.85, 5.2 S.D.) ng/g. Calculated levels of mercury exposure of breast fed babies indicated that 53% were above tolerable daily intakes (0.5 μg/kg body weight) recommended for adults by WHO. Mercury concentration in maternal hair was higher than in hair from breast-fed babies. Correlation analysis showed that mercury hair concentration in infants was significantly affected by maternal mercury contamination during pregnancy, but not during the post-natal breast-feeding period. The mercury concentration in milk was not significantly correlated with maternal or infants hair Hg. A statistically significant correlation was found only between maternal and infants hair mercury concentration (r=0.675; P=0.0001).

Selenium and breast-feeding

The objective of the present review is to discuss Se nutrition during breast-feeding, encompassing environmental and maternal constitutional factors affecting breast-milk-Se metabolism and secretion. A literature search of Medline and Webofscience was used to retrieve and select papers dealing with Se and breast milk. Although Se in natural foods occurs only in organic form, breast milk responds to organic and inorganic Se in supplements. Inorganic Se (selenite, selenate), which is largely used in maternal supplements, is not detectable in breast milk. The mammary-gland regulating mechanism controls the synthesis and secretion of seleno-compounds throughout lactation, with a high total Se level in colostrum that decreases as lactation progresses. Se appears in breast milk as a component of specific seleno-proteins and seleno-amino-acids in milk proteins that are well tolerated by breast-fed infants even in high amounts. Se in breast milk occurs as glutathione peroxidase (4-32 % total Se) > selenocystamine > selenocystine > selenomethionine. The wide range of breast-milk Se concentrations depends on Se consumed in natural foods, which reflects the Se content of the soils where they are grown. Se prophylaxis, either through soil Se fertilization or maternal supplements, is effective in raising breast-milk Se concentration. In spite of wide variation, the median Se concentration from studies worldwide are 26, 18, 15, and 17 microg/l in colostrum (0-5 d), transitional milk (6-21 d), mature milk (1-3 months) and late lactation (>5 months) respectively. Se recommendations for infants are presently not achieved in 30 % of the reported breast-milk Se concentrations; nevertheless Se status is greater in breast-fed than in formula-fed infants.

Selenium and mercury concentrations in some fish species of the Madeira River, Amazon Basin, Brazil.

Samples of 7 species of piscivorous, omnivorous, and herbivorous fish caught at 12 different sites on the Madeira River, Amazon Basin, were analyzed for selenium and mercury. Selenium was determined by anodic stripping voltammetry and mercury by cold vapor atomic absorption spectrophotometry. The means for selenium concentrations ranged from 0.49 to 3.11 nmol/g and for mercury from 0.41 to 6.66 nmol/g depending on the fish species. The molar ratios of Hg:Se increased according to the fish trophic level. Piscivorous species had the highest mean ratio (4.0) and herbivorous species the lowest (0.9). There was a positive and statistically significant correlation between selenium and mercury concentrations for the herbivorous species (r = 0.716;p = 0.0088) not seen for omnivororus and piscivorous species (r = -0.2032;p = 0.3407). These findings are significant for the fish-eating population of the Madeira River because the ingestion of mercury would always be in excess of selenium.

Maternal Smoking and Infant Feeding: Breastfeeding is Better and Safer

The rise in smoking rates among young women has implications for children’s health aggravated in lower social strata where infant morbidity and mortality rates are higher. The protection afforded by breastfeeding is beneficial to infants in rich and poor countries alike. Women (especially when young, uneducated, and unsupported) who are smokers constitute a risk group for abandoning breastfeeding; moreover, their bottle-fed newborns run a greater risk of morbidity and mortality. Bottle-feeding is attendant on maternal cigarette smoking. The advantages of breastfeeding over bottle-feeding are discussed with regard to systemic effects and the specific effects of cyanide (which can affect the iodine metabolism of infants) and nicotine derived from food and maternal smoking. Despite great strides in bans on smoking, public health policies should be designed to keep in perspective that breastfeeding is an effective tool to counterbalance the health disadvantages that under-privileged infants of smoking mothers face. This paper argues that infants born to smoking parents are better protected by breastfeeding than by formula feeding. Therefore, if public health policies cannot stop addicted mothers from smoking during pregnancy it is fundamental not to miss the chance of encouraging and supporting breastfeeding. The food and health inequalities of socially disadvantaged groups demand well crafted public-health policies to reduce the incidence of diseases and compress morbidity: these policies need to make it clear that breastfeeding is better and safer.

Fish consumption, mercury exposure and serum antinuclear antibody in Amazonians

Abstract Exposure to intrinsic Hg in fish was studied in Amazon populations with high prevalence of malaria disease. High fish-eater riverines were compared to urban (Manaus residents) low fish-eater riverines in regards to Hg exposure (hair-Hg) and serum antinuclear antibodies (ANA). Most riverines (99.0%) ate fish daily compared to only 3% of controls. Fish species high in MeHg was consumed more frequently (45.5%) by riverines than controls (18.8%). Mean hair-Hg (34.5 ppm) of riverines was significantly higher than controls (1.0 ppm). Although positive serum ANA was more frequently observed in riverine fish-eaters (12.4%) than controls (2.9%), there was no significant association between hair-Hg and ANA. High prevalence of malaria reporting among riverines was neither associated with Hg exposure nor with serum ANA. An autoimmune dysfunction is unlikely to occur as a result of MMHg exposure due to fish consumption.