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Currently, ethylmercury (EtHg) and adjuvant-Al are the dominating interventional exposures encountered by fetuses, newborns, and infants due to immunization with Thimerosal-containing vaccines (TCVs). Despite their long use as active agents of medicines and fungicides, the safety levels of these substances have never been determined, either for animals or for adult humans—much less for fetuses, newborns, infants, and children. I reviewed the literature for papers reporting on outcomes associated with (a) multiple exposures and metabolism of EtHg and Al during early life; (b) physiological and metabolic characteristics of newborns, neonates, and infants relevant to xenobiotic exposure and effects; (c) neurobehavioral, immunological, and inflammatory reactions to Thimerosal and Al-adjuvants resulting from TCV exposure in infancy. Immunological and neurobehavioral effects of Thimerosal-EtHg and Al-adjuvants are not extraordinary; rather, these effects are easily detected in high and low income countries, with co-exposure to methylmercury (MeHg) or other neurotoxicants. Rigorous and replicable studies (in different animal species) have shown evidence of EtHg and Al toxicities. More research attention has been given to EtHg and findings have showed a solid link with neurotoxic effects in humans; however, the potential synergic effect of both toxic agents has not been properly studied. Therefore, early life exposure to both EtHg and Al deserves due consideration.

Neurodevelopment as Gesell development scores (GDSs) in relation to mercury exposure in infants (<6 months of age) of one urban center and two rural villages, respectively, of fisherman and cassiterite miners. Mean total hair-Hg (HHg) concentrations of infants from Itapuã (3.95±1.8 ppm) were statistically (P=0.0001) different from those of infants from Porto Velho (3.84±5.5 ppm) and Bom Futuro (1.85±0.9 ppm). Differences in vaccine coverage among these populations resulted in significantly higher (P=0.0001) mean ethylmercury (EtHg) exposure in urban infants (150 μg) than in infants from either village (41.67 μg, Itapuã; 42.39 μg, Bom Futuro). There was an inverse significant (Spearman r=−0.2300; P=0.0376) correlation between HHg and GDS for infants from Porto Velho, but not for the rural infants from Bom Futuro (Spearman r=0.1336; P=0.0862) and Itapuã (Spearman r=0.1666; P=0.5182). Logistic regression applied to variables above or below the median GDS showed that EtHg exposure (estimated probability=−0.0157; P=0.0070) and breastfeeding score (estimated probability=−0.0066; P=0.0536) score were significantly associated with GDS. Conclusion. In nurslings whose mothers are exposed to different levels of fish-MeHg (HHg), a higher score of neurological development at six months was negatively associated with exposure to additional TCV-EtHg. Results should be interpreted with caution because of unaccounted variables.

The success of vaccination programs in reducing and eliminating infectious diseases has contributed to an ever-increasing number of vaccines given at earlier ages (newborns and infants). Exposure to low levels of environmental toxic substances (including metals) at an early age raises plausible concerns over increasingly lower neuro-cognitive rates. Current immunization schedules with vaccines containing aluminum (as adjuvant) are given to infants, but thimerosal (as preservative) is found mostly in vaccines used in non-industrialized countries. Exclusively, breastfed infants (in Brazil) receiving a full recommended schedule of immunizations showed an exceedingly high exposure of Al (225 to 1750  μ g per dose) when compared with estimated levels absorbed from breast milk (2.0  μ g). This study does not dispute the safety of vaccines but reinforces the need to study long-term effects of early exposure to neuro-toxic substances on the developing brain. Pragmatic vaccine safety needs to embrace conventional toxicology, addressing especial characteristics of unborn fetuses, neonates and infants exposed to low levels of aluminum, and ethylmercury traditionally considered innocuous to the central nervous system.

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 μg/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.

A simplified thiourea-based chromatography method, originally developed for methyl and inorganic mercury, was adapted to separate methylmercury (MeHg), ethylmercury (EtHg), and inorganic mercury (HgII) in infants' hair. Samples were weighed and leached with an acidic thiourea solution. Leachates were concentrated on a polymeric resin prior to analysis by Hg-thiourea liquid chromatography/cold vapor atomic fluorescence spectrometry. All but one sample showed small amounts of EtHg, and four of the six analyzed samples had proportionally higher HgII as a percent of total Hg. Breastfed infants from riverine Amazonian communities are exposed to mercury in breast milk (from high levels of maternal sources that include both fish consumption and dental amalgam) and to EtHg in vaccines (from thimerosal). The method proved sensitive enough to detect and quantify acute EtHg exposure after shots of thimerosal-containing vaccines. Based on work with MeHg and HgII, estimated detection limits for this method are 0.050, 0.10, and 0.10 ng g−1 for MeHg, HgII, and EtHg, respectively, for a 20-mg sample. Specific limits depend on the amount of sample extracted and the amount of extract injected.

Lederman et al. (2008) assessed Psychomotor Development Index (PDI) and Verbal and Full Intelligence Quotient Scores (VFIQS) (at 36 months of age for PDI and 48 months for VFIQS) as a function of prenatal mercury exposure (corrected for maternal fish intake during pregnancy) resulting from potential exposure after the World Trade Center (WTC) disaster. This timely and interesting study took into consideration maternal variables known to influence cord Hg (possibly reflecting fish consumption) and also controlled for most of the known maternal characteristics that could affect neuro-developmental outcomes. However, two of the most important variables in die context of infant exposure and neurodevelopment were left out of the model: early (pregnancy and postnatal) thimerosal-Hg exposure and the mode of feeding (Dorea 2007).

Tang et al. (2008) made a significant contribution to understanding the effects of prenatal exposure to coal-burning pollutants: Decrements in DQs [developmental quotients, measured by the Gesell Developmental Schedules] were significantly associated with cord blood levels of PAH-DNA adducts and lead, but not mercury.

Regular annual flooding of the Amazonian rivers changes the aquatic environment affecting fish feeding strategies. The Rio Madeira has been greatly impacted by deforestation for agricultural projects, damming for a hydroelectric power plant, and alluvial gold extraction. We studied fish-Hg concentrations within defined weight ranges of representative species at the top of the food web, comparing high and low water seasons. Selected piscivorous species (Cichla spp, Hoplias malabaricus, Pinirampus pirinampu, Serrasalmus spp) showed a large variation of Hg concentrations but only “traíra” (Hoplias malabaricus) showed a statistically significant difference between seasons. However, the bioaccumulation trends during high and low waters were similar for “tucunaré” (Cichla spp) and “traíra” (Hoplias malabaricus) but different for “piranhas” (Serrasalmus spp), “barba chata” (Pinirampus pirinampu) and the detritivorous Prochilodus nigricans. Fish-Hg bioaccumulation is species specific; changes in feeding strategies brought by flooding seasons can change the bioaccumulation pattern without systematically affecting the overall accrual of methylmercury in tertiary consumer species. It appears that naturally occurring Hg and the high sediment load of the Rio Madeira are secondary factors in the Hg bioaccumulation pattern of fish species at the top of the food chain.