Simultaneous determination of trace levels of ethylmercury and methylmercury in biological samples and vaccines using sodium tetra(n-propyl)borate as derivatizing agent

Degradation of organic mercury in high salt environments by a marine aerobic bacterium Alteromonas macleodii KD01

Mercury (Hg), particularly organic mercury, poses a global concern due to its pronounced toxicity and bioaccumulation. Bioremediation of organic mercury in high-salt wastewater faces challenges due to the growth limitations imposed by elevated Cl- and Na+ concentrations on microorganisms. In this study, an isolated marine bacterium Alteromonas macleodii KD01 was demonstrated to degrade methylmercury (MeHg) efficiently in seawater and then was applied to degrade organic mercury (MeHg, ethylmercury, and thimerosal) in simulated high-salt wastewater. Results showed that A. macleodii KD01 can rapidly degrade organic mercury (within 20 min) even at high concentrations (>10 ng/mL), volatilizing a portion of Hg from the wastewater. Further analysis revealed an increased transcription of organomercury lyase (merB) with rising organic mercury concentrations during the exposure process, suggesting the involvement of mer operon (merA and merB). These findings highlight A. macleodii KD01 as a promising candidate for addressing organic mercury pollution in high-salt wastewater.

Multiple low-level exposures: Hg interactions with co-occurring neurotoxic substances in early life

All chemical forms of Hg can affect neurodevelopment; however, low levels of organic Hg (methylmercury-MeHg and ethylmercury-EtHg in Thimerosal-containing vaccines, hereafter 'TCV') exposures during early life (pregnancy and lactation) co-occur with other environmental neurotoxic substances. These neurotoxicants may act in parallel, synergistically, or antagonistically to Hg. Nevertheless, the risks of neurotoxicity associated with multiple neuro-toxicants depend on type, time, combinations of exposure, and environmental and/or genetic-associated factors. Neurological developmental disorders, delays in cognition and behavioral outcomes associated with multiple exposures (which include Hg) may show transient or lasting outcomes depending on constitutional and/or environmental factors that can interact to neutralize, aggravate or attenuate these effects; often these studies are challenging to interpret. During pregnancy and lactation, fish-MeHg exposure is frequently confounded with the opposing effects of neuroactive nutrients (in fish) that lead to positive, negative, or no effects on neurobehavioral tests. In infancy, exposures to acute binary mixtures (TCV- EtHg and Al-adjuvants in infant immunizations) are associated with increased risks of tics and other developmental disorders. Despite the certitude that promulgates single environmental neurotoxicants, empirical comparisons of combined exposures indicate that Hg-related outcome is uneven. Hg in combination with other neurotoxic mixtures may elevate risks of neurotoxicity, but these risks arise in circumstances that are not yet predictable. Therefore, to achieve the goals of the Minamata treaty and to safeguard the health of children, low levels of mercury exposure (in any chemical form) needs to be further reduced whether the source is environmental (air- and food-borne) or iatrogenic (pediatric TCVs).

A Reliable Method to Determine Monomethylmercury and Monoethylmercury Simultaneously in Aqueous Samples by GC-CVAFS After Distillation

A reliable method for simultaneous determination of monomethylmercury (MeHg) and monoethylmercury (EtHg) in water by gas chromatography with cold vapor atomic fluorescence spectrometry was developed and validated. The experimental conditions, including derivatisation pH, distillation, and complexing agents, were optimized in detail. The absolute detection limits (3σ) were 0.007 ng/L as Hg for MeHg and 0.004 ng/L as Hg for EtHg. The relative standard deviation values (n = 6) for 0.1 ng/L of MeHg and EtHg were 2.7 and 2.1%, 1.0 ng/L of MeHg and EtHg were 6.0 and 6.9%, 4.4 ng/L of MeHg and EtHg were 2.8 and 2.7%, respectively. In addition, five different water samples were analyzed, including river water (RW), effluent wastewater (EW), seawater (SW), industrial wastewater (IW), underground water (UW), and the spiked recoveries of MeHg, were all greater than 85%, whereas EtHg was 86.0% in RW, 83.0% in EW, 87.0% in UW, 82.6% in SW, and 80% in IW. Formation of artefact MeHg and EtHg was studied during distillation. The level of artefact MeHg formed by methylation of Hg(II) during distillation varies from ~ 0.002 to 0.009% for river water and from ~ 0.002 to 0.004% for effluent wastewater, ethylation of Hg(II) was not observed. The method was validated for a variety of water sources with Hg(II) concentrations under 440 ng/L.

Partitioning behavior of heavy metals and persistent organic pollutants among feto-maternal bloods and tissues

Heavy metals and persistent organic pollutants (POPs), including Pb, Cd, T-Hg, MeHg, PCDD/Fs, PCBs, PBDEs, PCNs, and PBDD/Fs, were analyzed in 20 paired samples of cord blood, maternal blood, maternal urine, and placenta. The samples were collected from pregnant mothers and neonates from South Korea in 2010. The distribution of heavy metals among the samples varied with their physicochemical characteristics. The concentrations of Pb and Hg in the maternal and the cord blood samples were significantly correlated each other, implying efficient transplacental transport (TPT). Cd and Hg were accumulated in the placenta, forming protein conjugates, and T-Hg was higher in the cord blood samples than the maternal blood samples due to the binding affinity of Hg with fetal proteins. POPs generally showed the highest concentrations in the maternal serum samples, and the POPs levels in the cord serum and the placenta samples were dependent on the degree of halogenation. The TPT of POPs was seemingly related to lipoprotein transportation. Some PBDE congeners, however, showed their highest concentrations in the cord serum samples, suggesting an additional TPT mechanism. This is the first study to detect PCNs and PBDD/Fs in the cord serum samples, showing that the PCN levels were comparable to other POPs. According to the principal component analysis (PCA) results of the contaminant levels, POPs and heavy metals showed significantly different characteristics, whereas PBDEs had an intermediate attribute. Despite the limited number of participants, the comprehensive analysis of trace contaminants in the paired sample sets enabled us to infer the distribution and TPT mechanism of various contaminants.

Measurement of mercury species in whole blood using speciated isotope dilution methodology integrated with microwave-enhanced solubilization and spike equilibration, headspace-solid-phase microextraction, and GC-ICP-MS analysis

A biomonitoring method was developed for the determination of inorganic-, methyl-, and ethylmercury (Hg(2+), CH3Hg(+), and C2H5Hg(+), respectively) in whole blood by triple-spiking speciated isotope dilution mass spectrometry (SIDMS) using headspace (HS) solid-phase microextraction (SPME) in combination with gas chromatographic (GC) separation and inductively coupled plasma mass spectrometric (ICP-MS) detection. After spiking the blood sample with isotopically enriched analogues of the analytes ((199)Hg(2+), CH3(200)Hg(+) and C2H5(201)Hg(+)), the endogenous Hg species were solubilized in 2.0 mol L(-1) HNO3 and equilibrated with the spikes using a microwave-enhanced protocol. The microwaved sample was treated with a 1% (w/v) aqueous solution of sodium tetrapropylborate (buffered to pH 5.2), and the propylated Hg species were sampled in the HS using a Carboxen/polydimethylsiloxane-coated SPME fiber. The extracted species were thermally desorbed from the fiber in the GC injection port and determined by GC-ICP-MS. The analytes were quantified, with simultaneous correction for their method-induced transformation, on the basis of the mathematical relationship in triple-spiking SIDMS. The method was validated using a bovine blood standard reference material (SRM 966, Level 2). Analysis of human blood samples demonstrated the accuracy and reproducibility of the method, which can detect the Hg species down to 30 pg g(-1) in blood. The validity of the analytical results found for the blood samples was demonstrated using mass balance by comparing the sum of the concentrations of the individual Hg species with the total Hg in the corresponding samples; the latter was determined by isotope dilution mass spectrometry (IDMS) after decomposing the blood using EPA Method 3052 with single-spiking.

Prenatal methylmercury exposure through maternal rice ingestion: insights from a feasibility pilot in Guizhou Province, China

Maternal hair and blood were investigated as biomarkers for prenatal methylmercury (MeHg) exposure among seventeen mothers recruited at parturition in Wanshan, Guizhou Province, China, where rice ingestion was the primary MeHg exposure pathway and atmospheric mercury (Hg) levels were elevated. For all three trimesters (n = 51), hair total Hg (THg) and MeHg concentrations ranged from 0.27 to 4.9 μg/g (median: 0.96 μg/g) and 0.077 to 2.3 μg/g (median: 0.43 μg/g), respectively, while blood THg levels ranged from 1.7 to 11 μg/L (median: 3.0 μg/L, n = 17). Despite adequate hair washing procedures, median %MeHg (of THg) was 37% (range: 14-89%, n = 51), indicating exogenous inorganic Hg(II) contamination or incorporation of elemental Hg (Hg(o)) into the hair shaft were important. Rice MeHg levels (n = 17) were highly correlated with blood THg (r(2) = 0.66) compared to hair MeHg (r(2) = 0.31) (when variables were log10-transformed), suggesting blood THg was a more preferable biomarker for prenatal MeHg exposure within this population.

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. EtHg's 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).

Automated speciation of mercury in the hair of breastfed infants exposed to ethylmercury from thimerosal-containing vaccines

A simplified thiourea-based chromatography method, originally developed for methyl and inorganic mercury, was adapted to separate methylmercury (MeHg), ethylmercury (EtHg), and inorganic mercury (Hg(II)) 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 Hg(II) 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 Hg(II), estimated detection limits for this method are 0.050, 0.10, and 0.10 ng g⁻¹ for MeHg, Hg(II), and EtHg, respectively, for a 20-mg sample. Specific limits depend on the amount of sample extracted and the amount of extract injected.

Speciation of methyl- and ethyl-mercury in hair of breastfed infants acutely exposed to thimerosal-containing vaccines

BACKGROUND

Different chemical forms of mercury occur naturally in human milk. The most controversial aspect of early post-natal exposure to organic mercury is ethylmercury (EtHg) in thimerosal-containing vaccines (TCV) still being used in many countries. Thus exclusively breastfed infants can be exposed to both, fish derived methylmercury (MeHg) in maternal diets and to EtHg from TCV. The aim of the study is to evaluate a new analytical method for ethyl and methyl mercury in hair samples of breastfed infants who had received the recommended schedule of TCV.

METHODS

The hair of infants (<12 months) that had been exposed to TCV (Hepatitis B and DTaP) was analysed. A method coupling isothermal gas chromatography with cold-vapor atomic fluorescence spectrometry was used for MeHg which can also speciate EtHg in biological matrices.

RESULTS

In 20 samples of infants' hair, all but two samples showed variable amounts of MeHg (10.3 to 668 ng/g), while precise and reliable concentrations of EtHg (3.7 to 65.0 ng/g) were found in 15 of the 20 samples. A statistically significant inverse association (r=-05572; p=0.0384) was found between hair-EtHg concentrations and the time elapsed after the last TCV shot.

CONCLUSIONS

The analytical method proved sensitive enough to quantify EtHg in babies' hair after acute exposure to thimerosal in vaccine shots. Provided that the mass of hair was above 10mg, organic-mercury exposure during early life can be speciated, and quantified in babies' first hair, thus opening opportunities for clinical and forensic studies.

Toxicokinetics of mercury after long-term repeated exposure to thimerosal-containing vaccine

The preservative thimerosal contains ethyl mercury (EtHg). Concerns over possible toxicity have re-emerged recently due to its presence in (swine and other) flu vaccines. We examined the potential accumulation of mercury in adults given repeated injections of a thimerosal-preserved vaccine for many years. Fifteen female patients were recruited from an outpatient clinic running a clinical trial with repeated injections (1 ml every 3-4 weeks) of a staphylococcus toxoid vaccine containing 0.01% thimerosal to treat chronic fatigue syndrome. Fifteen untreated female patients with the same diagnoses served as controls. Blood samples were taken before injecting the vaccine, 1 day later, about 2 weeks later, and just before the next injection. In the 15 controls, samples were taken twice. Blood was analyzed for total mercury and EtHg. The toxicokinetics were assessed for each patient separately as well as with a population-based pharmacokinetic model. Total mercury in blood increased on Day 1 in all treated patients (median: 0.33, range: 0.17-1.3 μg/l), as did EtHg (median: 0.14 μg/l, range: 0.06-0.43 μg/l). After a few weeks, levels were back to normal and similar to those in controls. Levels of methyl mercury (MeHg; from fish consumption) were much higher than those of EtHg. After exclusion of an outlier, the mean half-life in a population-based model was 5.6 (95% CI: 4.8-6.3) days. The results indicate that mercury from thimerosal is not accumulated in blood in adults. This is in accordance with short half-lives and rapid metabolism of EtHg to inorganic mercury.