Mercury, an invisible problem

Mercury is a metal, liquid at ambient temperature and pressure. This element is present in the environment in several states, such as elemental mercury, and inorganic or organic species, like methylmercury. Mercury is present in nature due to natural processes like rock erosion and volcanic activity. However, most Hg existent derives from human activity. This compound is bioamplified through the food chain.

Mercury is a toxic element, and its presence in the human organism can lead to damage in the nervous and cardiovascular systems, for example. This compound can be extremely dangerous due to the human body’s incapacity to filter/excrete it. As such, absorbed mercury will accumulate in our bodies.

The dangers associated with mercury contamination led to the Minamata Convention, which attempts to safeguard human and environmental health against this element’s debilitating effects.

When faced with this worrying issue, we developed a study in which we looked to evaluate the mercury contamination of students in our school.

Problem identification

The element mercury is a metal, liquid at temperature and environment pressure, silver-colored, with a low solubility in water and lipids. It may appear in diverse forms and in a high number of chemical types, mainly like elementary mercury, organic and inorganic types.

This element is found as expected in environment and it can come from the erosion of rocks and volcanic activity, among other natural processes. However, the majority of mercury in the environment comes from processes related with human activity, among them the use of fossil combustibles – especially coal, power plants, mineral industries (gold and mercury mines), pesticides and medical equipment (UNEP, 2002; WHO, 2007; Sousa et al., 2013).

Apart from the chemical versatility of this compound, mercury, as its types, has the power to affect the humans, directly or indirectly. It can cause different symptoms/diseases in several organs and systems of the body, such as nervous system, kidneys, lungs and heart (respiratory or cardiovascular diseases). For example, methyl mercury is usually associated to neurological problems with the possibility of causing diverse symptoms, such as sensory troubles, the narrowing of the field of vision, speech difficulties, losing one’s balance, amongst other effects (Sousa & Barbosa, 2000).

This is due to the fact that methyl mercury (picture 1) is highly reactive and toxic to the organisms, since it has the capacity of surpassing the blood-brain barrier (BHE). Besides, mercury, especially methyl mercury, is a biomagnified compound along the food chain, mainly in marine environments (Watras & Bloom, 1992). So, consuming several organisms with low mercury concentrations will expose the beings at the top of the food chain to relatively high mercury concentrations.

This includes fish that, as part of our food, are one of the main sources of the human exposure to this type of mercury (Issaro et al., 2009). Methyl mercury, in high concentrations in blood, can cause mercury poisoning, a serious disease which can lead to death (Clarkson & Magos, 2006). This disease affects the human nervous system, causing neurological troubles, such as losing the sensibility in upper and lower ends or the coordination, diminishing of vision or hearing and slurred speech.

In children the neurological system isn’t completely developed and the methyl mercury can cross the blood-brain barrier. It is documented the relationship between the methyl mercury and the decreasing of the cognition power in children in development (Oken et al., 2005). So, it is necessary to monitor the child’s development and to prevent mercury exposure (WHO, 2007).

Chemical composition of methylmercury

Adapted from https://inhabitat.com/mercury-found-in-california-fog-may-threaten-the-food-chain/mercury-contamination-through-food-chain/

Sources of exposure to mercury

Adapted from http://www.formfunctionclinic.com/brampton/risks-of-high-levels-of-mercury/

The human being is exposed to mercury both in the domestic environment and at work.

UN Environment Programme, Time to Act, 2013.

Population in general is exposed to mercury through the ingestion of contaminated food (mainly predatory fish) as well as the exposure to several consuming products containing mercury, such as cosmetics, household products and pharmaceuticals. It can also be an involuntary exposure to products which contain mercury in their composition, such as batteries, electric and electronic equipments, fluorescent lamps and medical equipments (for example, thermometers and sphygmomanometers – OMS, 2007).

There are many factors that influence the presence of mercury in the organism, such as the residence area, the food and the consuming/use of substances (some medicine, hair dyes, cosmetics, etc. – Castaño et al., 2015).

Although the World Health Organization (WHO) has concluded that there aren’t mercury levels called secure, it was established an acceptable limit of ingestion of mercury per day 0,2 ug kg-1 of body weight (WHO, 2007).

Mercury Exposure and Contamination

Methyl mercury, in high concentrations in blood, can cause mercury poisoning, a serious disease which can lead to death (Clarkson & Magos, 2006). This disease affects the human nervous system, causing neurological troubles, such as losing the sensibility in upper and lower ends or the coordination, diminishing of vision or hearing and slurred speech.

In children the neurological system isn’t completely developed and the methyl mercury can cross the blood-brain barrier. It is documented the relationship between the methyl mercury and the diminishing of the cognition power in children in development (Oken et al., 2005).

Effects on Health:

Long-term exposure to mercury affects the central nervous system. Among the effects are increased excitability, irritability, excessive shyness, tremors or shakiness, paresthesia ( a sensation of pricking on the skin), blurred vision, malaise, speech difficulties, constriction of the visual field, memory loss, and kidney disease. Effects on the gastrointestinal tract and respiratory system have also been noted from acute inhalation of the elementary mercury.

Short-term exposure to high levels of mercury will have similar effects as the long-term exposure, but full recovery is more likely after short-term exposure, once the body clears itself of the contamination.

Mercury can also effect the developing fetus. Infants born from women exposed to high levels of mercury exhibited mental retardation, ataxia, constriction of visual field, blindness, and cerebral paralysis.

Study: Assessment of the levels of mercury in students aged 12 to 18

A study was developed, trying to evaluate the mercury contamination by means of the analysis of the levels of this element in the human hair, since this is a matrix validated to monitor the mercury concentrations in the human being. Consumer products were also analyzed (food; hygienic and cosmetic products; office objects).

The process of collecting biological samples (hair) was approved by the Pedagogical Board of Colégio Valsassina and authorized by the National Committee of Data Protection. All the paralysis sign an informed consent. All the data collected for this study were codified and treated in a confidential way. The sample was formed by 75 individuals (29 – male; 46 – female), aged between 12 and 18, with an average age of 14.76 ± 1.63.

The experimental protocol followed the recommendations expressed by the project COPHES: a European project aiming at the harmonizing of the collection and treatment of samples for studies of human bio-monitoring.

A sample of hair of each individual was collected. An questionnaire was also fulfilled with several questions, such as birth date, gender, weight, height, food habits, residence area, characteristics of the hair and its length.

The technique used to quantify the mercury concentration in the collected samples was the direct analysis by thermal decomposition, using NIC (Nippon Instruments Corporation) Direct Thermal Decomposition Mercury Analyser MA-3000, which allows the analysis of the mercury concentration in solid samples.

The 82 analyzed hair samples revealed medium mercury contents of 1150.10 +- 685.34 ng g-1. The concentrations varied between 12.6 and 3314.74 ng g-1.Comparing with the reference value of the US EPA (United States Environmental Protection Agency) for these analyses, 1000 ng g-1, 32 individuals, representing 46% of the studied population, present [Hg] higher than this reference value; from this on, it is considered the possibility of risks to the human health. In turn, when compared with the reference value of the WHO (World Health Organization), 2000 ng g-1, 11,42 % (8 individuals) present values higher than the referred limit.

We also evaluated the relationship between the mercury level and the gender, age, residence area (urban/rural), type of fish consumed and IMC-BMI. The analyzed consumer products revealed levels of mercury that should be carefully analyzed (food: n = 43; average of 0.39ng g-1; office items: n = 4; average 3.93 ng g-1).

With the data obtained in this investigation and its innovative character, since there are no other studies for this age level (12 to 18), some actions were recommended. Considering that the general population is exposed to mercury, namely through the ingestion of contaminated food (specially predatory fish), it is advisable to promote campaigns for educating and sensitizing correct food behaviors, aiming at a good choice of species to be consumed, as well as more monitoring studies of mercury levels using hair samples of lower age stages.

Results (hair samples)

Product analysis

Mercury Poisoning Prevention

Prevention of mercury poisoning is difficult if the source of the mercury is unknown. Consequently, prevention of mercury poisoning begins with identifying the potential or known sources and stopping production or isolating the toxin so none will come in contact with people.

At Home

At home, there are a few mercury- containing items (for example, thermometers, medical devices, some disinfectants, fluorescent light bulbs) that potentially can be the source of mercury poisoning. People need to read the labels on products to see if they contain mercury, have warning labels about potential toxicity, or have directions about how to dispose of a broken or non-useable product.

Amalgam Fillings

People are also concerned about mercury found in dental amalgam fillings. Dental amalgam is a dental filling material used to fill cavities caused by tooth decay. It has been used for more than 150 years in hundreds of millions of patients around the world.

Dental amalgam is a mixture of metals, consisting of liquid (elemental) mercury and a powdered alloy composed of silver, tin, and copper. Approximately 50% of dental amalgam is elemental mercury by weight.

Dental amalgam contains elemental mercury. So, it releases low levels of mercury in the form of a vapor that can be inhaled and absorbed by the lungs. High levels of mercury vapor exposure are associated with adverse effects in the brain and the kidneys.

FDA (U.S. Food and Drug Administration) has reviewed the best available scientific evidence to determine whether the low levels of mercury vapor associated with dental amalgam fillings are a cause for concern. Based on this evidence the FDA considers dental amalgam fillings safe for adults and children ages 6 and above. If you believe you have an allergy or sensitivity to mercury or any of the other metals in dental amalgam (such as silver, tin, or copper), you should discuss treatment options with your dentist.

Vaccines

Another source of concern by people is the use of thimerosal, a mercury-containing preservative used in vaccine preparations. Except for some influenza vaccines, it is not being used in most vaccines. However, the amount of mercury in thimerosal is very low.

Fish and Shellfish

Fish are important in a healthy diet. They are a lean, low-calorie source of protein. However, some fish may contain mercury or other harmful chemicals at sufficiently high levels to be a concern.

To prevent people from getting toxic mercury levels from eating seafood it is necessary to know that the levels of mercury vary according to the species of fish. To enjoy the benefits of eating fish while minimizing exposure to mercury, we recommend:

1

Do not eat shark, swordfish, king mackerel, or tilefish because they contain high levels of mercury.

2

Eat up to 12 ounces, 340 g, (two average meals) a week of a variety of fish and shellfish that are lower in mercury.

3

Five of the most commonly eaten fish that are low in mercury are shrimp, canned light tuna, salmon, pollock, and catfish.

4

Another commonly eaten fish, albacore ("white") tuna has more mercury than canned light tuna. So, when choosing your two meals of fish and shellfish, you may eat up to 6 ounces (one average meal) of albacore tuna per week.

5

Check local advisories about the safety of fish caught by family and friends in your local lakes, rivers, and coastal areas. If no advice is available, eat up to 6 ounces (one average meal) per week of fish you catch from local waters, but don't consume any other fish during that week.

6

Women who are trying to become pregnant, who are pregnant or are breastfeeding should be especially careful about following these suggestions as the fetus, neonate and infant brains and spinal cord seems especially sensitive to all forms of mercury poisoning.

Adapted from https://www.organics.org/mercury-in-seafood-which-seafood-is-safe-to-eat/

Key facts

Mercury is a naturally occurring element that is found in air, water and soil.

Exposure to mercury – even small amounts – may cause serious health problems, and is a threat to the development of the child in utero and early in life.

Mercury may have toxic effects on the nervous, digestive and immune systems, and on lungs, kidneys, skin and eyes.

Mercury is considered by WHO as one of the top ten chemicals or groups of chemicals of major public health concern.

People are mainly exposed to methylmercury, an organic compound, when they eat fish and shellfish that its contaminated with mercury.

Methylmercury is very different from ethylmercury. Ethylmercury is used as a preservative in some vaccines and its not toxic as methylmercury.

The team

Afonso Mota

Bernardo Alves

João Leal

He is the shortest of us but had a huge contribution on our work. He is our team leader and in his spare time he's breaking ankles on the football pitch.
Bernardo is sort of sedentary. He is the only one of our group who doesn't play a sport. At least he has time to work on our project! In the future, he wants to be a doctor, and we believe he has all the capabilities to achive his dreams
The person who thinks they're funny when they aren't. He is also a top tennis player and a great colleague and friend, and an integral part of our group!
We appreciate all the support and guidance from Ana Catarina Sousa, PhD, Researcher, University of Beira Interior, Faculty of Health Sciences. Without its presence and availability it would not be possible to develop the project.
We are also grateful to the University of Beira Interior, Faculty of Health Sciences, Portugal, who welcomed us in their laboratories, to carry out the analysis of the samples.

Mercury: an invisible problem

Links

Fish calculator

Minamata Convention on Mercury

Minamata Convention on Mercury (documents)

United States Environmental Protection Agency (Mercury)

USEPA (Mercury)

WHO

European Commission (Mercury)

European Commission (Mercury/Minamata Convention)

Young Reporters for environmental (Portugal)