8 research outputs found
Inter-individual variations of human mercury exposure biomarkers: a cross-sectional assessment
BACKGROUND: Biomarkers for mercury (Hg) exposure have frequently been used to assess exposure and risk in various groups of the general population. We have evaluated the most frequently used biomarkers and the physiology on which they are based, to explore the inter-individual variations and their suitability for exposure assessment. METHODS: Concentrations of total Hg (THg), inorganic Hg (IHg) and organic Hg (OHg, assumed to be methylmercury; MeHg) were determined in whole blood, red blood cells, plasma, hair and urine from Swedish men and women. An automated multiple injection cold vapour atomic fluorescence spectrophotometry analytical system for Hg analysis was developed, which provided high sensitivity, accuracy, and precision. The distribution of the various mercury forms in the different biological media was explored. RESULTS: About 90% of the mercury found in the red blood cells was in the form of MeHg with small inter-individual variations, and part of the IHg found in the red blood cells could be attributed to demethylated MeHg. THg in plasma was associated with both IHg and MeHg, with large inter-individual variations in the distribution between red blood cells and plasma. THg in hair reflects MeHg exposure at all exposure levels, and not IHg exposure. The small fraction of IHg in hair is most probably emanating from demethylated MeHg. The inter-individual variation in the blood to hair ratio was very large. The variability seemed to decrease with increasing OHg in blood, most probably due to more frequent fish consumption and thereby blood concentrations approaching steady state. THg in urine reflected IHg exposure, also at very low IHg exposure levels. CONCLUSION: The use of THg concentration in whole blood as a proxy for MeHg exposure will give rise to an overestimation of the MeHg exposure depending on the degree of IHg exposure, why speciation of mercury forms is needed. THg in RBC and hair are suitable proxies for MeHg exposure. Using THg concentration in plasma as a measure of IHg exposure can lead to significant exposure misclassification. THg in urine is a suitable proxy for IHg exposure
Mercury exposure during early human development
People are exposed to methylimercury (MeHg) mainly via consumption of
fish, especially large predatory fish species. Inhaled mercury vapour
(Hg0) released from dental amalgam fillings is the main source of
exposure to inorganic mercury (I-Hg). In the body, a small fraction of
MeHg is demethylated to inorganic He while most Hg0 is oxidized to Hg2+.
Both MeHg and Hg2+ are neurotoxic, especially for the developing brain.
The aim of the present thesis was to increase the knowledge about the
exposure to MeHg and I-Hg in Swedish women of childbearing age, the
transport to the fetus and infant and to evaluate possible associations
between Se, an antioxidant reported to protect against Hg toxicity; and
the different forms of Hg.
Hg exposure during pregnancy was studied by determination of total Hg in
maternal hair and MeHg and I-Hg in maternal blood. Fetal exposure was
assessed by MeHg and I-Hg in cord blood. Infant exposure was assessed by
MeHg and I-Hg in infant blood and total Hg in breast milk. The
concentrations of MeHg and I-Hg were determined by cold vapour atomic
fluorescens spectrophotometry (CVAFS). Se concentrations in scrum or
whole blood were analysed by graphite furnace atomic absorption
spectrophotometry (GFAAS).
The exposure to I-Hg was mainly as Hg0 from dental amalgam fillings with
low exposure from oilier sources. The concentration of I-Hg in cord blood
was about the same as in maternal blood and increased with increasing
number of maternal dental amalgam fillings. This shows that a substantial
fraction of Hg0 passes the placenta to the fetus before being oxidized to
Hg2+. Also, I-Hg accumulated in the placenta in relation to the number of
amalgam filings. The use of amalgam in dentistry is decreasing.
MeHg exposure was highly dependent on fish consumption in general, but
consumption of freshwater fish and certain marine species e.g. swordfish
and tuna contributed more to the exposure. MeHg in cord blood increased
with increasing maternal fish consumption. It was almost twice the
concentration in maternal blood, supporting an active transport of MeHg
across the placenta. Although, the average exposure to MeHg was
relatively low, there was quite a range. A small fraction of women
recruited because of high fish consumption had Hg concentrations
exceeding the RfD (U.S. EPA) and PTWI (JECFA), corresponding to a daily
intake of0. 1-0.2 µg MeHg/kg bw. Thus, there seems to be a fairly narrow
margin of safety for increased risk of neurodevelopmental effects in
fetus of women with high fish consumption unless they decrease their
intake of certain fish species before being pregnant. It can be concluded
that the recently updated dietary advisories on fish consumption for
pregnant and lactating women and women planning pregnancy are justified
and necessary as long as MeHg levels in fish are elevated. There was a
good compliance to the dietary advisories regarding fish consumption
during pregnancy but it is important that the advisories reach all women
planning pregnancy, so they can decrease their consumption of certain
fish species to avoid early fetal exposure. However, it is also important
to emphasize the benefits of fish consumption. It is not known to what
extent the positive effects of fish consumption may outweigh the negative
effects of MeHg. Infant exposure to I-Hg and MeHg was lower than the
prenatal exposure. Total Hg concentrations in breast milk decreased
during the first three months postpartum. I-Hg seems to be more easily
transported to breast milk than MeHg. Still, MeHg in breast milk may
contribute more to infant exposure, because of higher gastrointestinal
absorption. Infant blood MeHg decreased until 13 weeks of age indicating
that infants are able to excrete MeHg taken up during fetal life,
contrary to previous believes.
No associations between Se and the different forms of Hg were observed in
the placenta and Se did not affect the accumulation or transport of I-Hg
or MeHg in placenta. The concentration of Se in serum decreased during
the course of pregnancy. Probably, this can partly be explained by a
prioritized fetal transport and need of Se for placental functions
Hälsorelateradmiljöövervakning(HÄMI) : – en utvärdering av programområdet
Hälsorelaterad miljöövervakning (HÄMI) startade i början av 1990-talet inom ramen för Naturvårdsverkets miljöövervakning. Syftet med programområdet är att övervaka hälsoeffekter som kan kopplas till miljön. För att kunna göra detta utförs bland annat undersökningar där halter av miljöföroreningar i blod, bröstmjölk, urin och luft mäts. Även studier av astmatikers besvär till följd av luftföroreningar utförs. Denna rapport är en utvärdering av det arbete som gjorts inom HÄMI och hur verksamheten kan utvecklas för att svara ännu bättre mot kommande utmaningar och krav
Hälsorelateradmiljöövervakning(HÄMI) : – en utvärdering av programområdet
Hälsorelaterad miljöövervakning (HÄMI) startade i början av 1990-talet inom ramen för Naturvårdsverkets miljöövervakning. Syftet med programområdet är att övervaka hälsoeffekter som kan kopplas till miljön. För att kunna göra detta utförs bland annat undersökningar där halter av miljöföroreningar i blod, bröstmjölk, urin och luft mäts. Även studier av astmatikers besvär till följd av luftföroreningar utförs. Denna rapport är en utvärdering av det arbete som gjorts inom HÄMI och hur verksamheten kan utvecklas för att svara ännu bättre mot kommande utmaningar och krav