L23 - Mercury Microbes Flashcards
What is inorganic mercury?
- Low absorption (0.01 – 7%
avg) - People become exposed
through their occupation.
What is organic mercury?
- High absorption (>90%)
- Primarily a central nervous
system toxin - Half-life of 50-70 days
- People may be exposed
through their diet (tuna)
What are the health effects of mercury exposure?
- Inorganic mercury and methyl-mercury are toxic to the central and peripheral nervous systems.
- loss of physical coordination
- difficulty in speech
- hearing impairment
- blindness
- death
- Children may be affected if they had been exposed in-utero through their mothers’
ingestion
What are the factors that determine whether health effects occur and their severity?
- the dose
- the age or developmental stage of the person exposed
- the duration of exposure
- the route of exposure (inhalation, ingestion or dermal contact)
What is bioaccumulation?
- Concentration of a toxic element increases as you move up the food chain (this is why they tell you not to eat tuna, as it would contain a lot of mercury)
- Sardines are a amazing source of omega 3 and fatty acids, and also contain very little mercury
Minamata disaster? 1932-1968
- Minamata is a small town on the coast of the Shiranui Sea in Japan.
- Because of its location, the local population living eat a lot of fish as part of their diet.
- Industrial wastewater, containing methyl-mercury, from a petrochemical plant was released into Minamata Bay from 1932 to 1968.
- 2,265 victims had been officially recognized as having Minamata
disease (neurological syndrome caused by severe mercury
poisoning). - People of reported a number of issues related to their nervous system
- numbness in their limbs and lips.
- difficulty hearing or seeing.
- shaking (tremors) in their arms and legs,
- shouting uncontrollably
- Women gave birth to poisoned babies with severe deformities.
How does mercury enter the environment?
- Mercury occurs naturally in the Earth’s crust
- It is naturally released into the environment from volcanic activity & weathering of rocks
Human activity is the main cause of mercury releases…
- Combustion of coal through mining
- Reservoirs of mercury in soils, water, sediments…
- Humans release inorganic mercury and then microbes convert it to organic mercury
How does mercury (Hg) turn into methyl-mercury (CH3Hg)?
Methylmercury is formed from inorganic mercury by the action of bacteria that live in aquatic systems including lakes, rivers
wetlands, sediments, soils and open ocean.
Why they do this is not really well-understood?
- They don’t use mercury as an electron donor or acceptor…
- Microbial-driven process: heterotrophic microbes that break down organic carbon compounds for cellular growth and energy.
Enrichment of mercury happening in all of these reservoirs for the past hundred of years… Humans’ exposure to mercury will be through the consumption of commercial fish
- Tuna
- Swordfish
- Pollock
When did we start catching on to this?
- 1969: “It is possible that living organisms have the capacity to methylate mercury compounds present in pollution”
- 1990s: Focus on microbial sulfate reduction in anoxic sediment
What are microbial sulfate reducers?
- Heterotrophs (obtain energy from eating organic compounds)
- Live in anaerobic environments (low or no O2)
- Use sulfate as an electron acceptor instead of oxygen (breathe in sulfate instead of oxygen)
- Key methylators
- Genes responsible for methylation are found in many different kinds of microbes (e.g. methanogens) not just sulfate reducers.
Hydrodams and methymercury
- Dams create artificial lakes, a flooded area.
- The mercury trapped in the soil is flooded and mobilized
- It turns into methylmercury because of the microbes in the water.
