θειομερσάλη, Υδράργυρος

Mercury, quicksilver or hydrargyrium (Hg) is a toxic metal that, in its various forms (metallic or elemental, inorganic compounds and organic compounds) behaves as an environmental pollutant harmful to health, with neurological and renal toxicity. ^{(MedlinePlus 2021, WHO/WHO 2017, ATSDR 2015 and 2012}

The bioavailability of mercury is highly variable depending on its state ^{(Hale, MedlinePlus 2021, ATSDR 2012)}:

• Metal or elemental Hg (from thermometers, dental amalgams, fluorescent bulbs): 0.01% by the oral route and > 80% by inhalation.
• Inorganic Hg from Hg disk batteries: 7-15% by oral route
• Organic Hg (phenylmercury, methylmercury from contaminated fish and shellfish, disinfectants such as thimerosal, mercurochrome): 90% by oral route

The main route of human exposure is the consumption of fish and shellfish contaminated with methylmercury, an organic compound present in these foods. Methylmercury is very different from ethylmercury. Ethylmercury is used as a preservative in some vaccines and does not pose a health risk. ^{(WHO 2017)}

According to several authors ^{(Hale, Yusà 2017, Al-Saleh 2015, Pitkin 1976)}, expert committees (FAO, WHO, USA-EPA, EFSA, CDC) establish :

• A maximum concentration in breast milk of 1.7 μg/L
• A maximum tolerable weekly intake of 4 μg/kg for Hg metal and 1.6 μg/kg/week for methylmercury
• A maximum hair concentration of 1 to 1,9 μg/g
• A maximum 24-hour urine or blood concentration of 5 μg/L

Elevated amounts of mercury in the body are mainly associated with the consumption of fish and offa^{l (Freire 2022, Marques 2016, Al-Saleh 2015, Vieira 2013, Barghi 2012, Orün 2012, Drexler 1998)} and to a much lesser extent and without clinical implications with the use of dental amalgams ^{(Rebelo 2017, Al-Saleh 2015, Vieira 2013, Jimenez 2013 Barghi 2012, Norouzi 2012, Richardson 2011, Roberts 2009,US-FDA 2009, da Costa 2005, Ursinyova 2005, Ekstrand 1998, Drexler 1998, Klemann 1990)}, thimerosal-containing vaccines ^{(Marques 2007)} and, in some countries to the consumption of cereals and vegetables ^{(Cherkani 2021, Rebelo 2017)}, of polyvitamins and lipstick use ^{(Cherkani 2021)} and of pollution from gold mining. ^{(Barbosa 1998)}

With elevated levels of Hg in breast milk (mean 2.6 μg/L), the mean weekly Hg intake for the infant was half the maximum tolerable (Rebelo 2017), but was higher in some infants whose mothers had very high levels (mean 3.6 μg/L) of Hg in breast milk. ^{(Cherkani 2021, Norouzi 2012)}

No neurodevelopmental impairment has been seen in infants breastfed for 6-24 months by mothers with very high hair Hg levels (12 μg/g) due to high fish consumption. ^{(Marques 2016)}

No association has been found between Hg in breast milk and Hg in urine and hair of infants:  Infants are exposed to maternal Hg during pregnancy, not during lactation. ^{(Al-Saleh 2015, Barbosa 1998).}

Fish consumption, due to its content of omega-3 fatty acids (DHA and EPA), is very beneficial for the health of the mother and the health and neurodevelopment of the infant. Fish with a very low mercury content (salmon, trout, herring, anchovy, sardine) should be chosen, tilefish, shark, swordfish and mackerel should be avoided and tuna consumption should be limited to 170 g per week. ^{(DGA 2010)}

Breastfeeding is contraindicated in case of acute or chronic poisoning with compatible clinical symptoms and/or elevated levels of Hg in 24-hour urine or breast milk. Mild exposure due to fish consumption, dental amalgams ^{(US-FDA 2021 and 2017, Ekstrand 1998, Drasch 1998, Klemann 1990)}, thimerosal-containing vaccines, Hg-containing lamps, does not contraindicate breastfeeding.

OCCUPATIONAL HAZARD

The R-risk phrases or Hazard H-phrases and precautionary P-phrases on the labelling that relate to breastfeeding are (INSHT 2022, UN 2011, EC Regulation 2008):

• H362 (ant. R64): 'May harm breastfed infants'.
• P263: "Avoid contact during pregnancy and lactation".

Other phrases to consider are:

• H350 (ant.R45 and R49): "May cause cancer""
• H351 (ant. R40): "Possible carcinogenic effects"
• H370 (ant. R39): "Causes damage to organs"
• H371 (ant. R68): "May cause damage to organs".
• H372 (ant R48): Same as H370, but "after prolonged or repeated exposure"
• H373 (ant R33): Same as H371, but "after prolonged or repeated exposure".

As the Hg MSDS contains the phrases H372 and H373 ^{(INSHT 2022)}, the exposed breastfeeding mother should be moved from her workstation. 

The benefits of breastfeeding outweigh the risk from low levels of environmental contaminants in human milk, in many cases lower than in cow's milk or other foods. ^{(Diaz 2013).}

Informed choice is based on an assessment of the known and unknown risks of artificial feeding against the potential but unproven risks of chemical contamination of breastmilk. ^{(Pronczuk 2002)}

See below the information of this related product:

• Dental Filling (Fairly safe. Mild or unlikely adverse effects. Compatible under certain circumstances. Follow-up recommended. Read Commentary.)