Lecture 21

Question 1

What are the two types of mercury that determine health impacts?

Answer 1

1. Inorganic mercury :
   - low absorption
   - exposed through occupation
2. Organic mercury (toxic kind):
   - high absorption
   - exposed through diet
   - primarily a central nervous system toxin
   - half life 50-70 days

Question 2

What are the health effects of mercury exposure?

Answer 2

Inorganic mercury and methylmercury are toxic to the central and peripheral nervous systems.

Question 3

What are the factors that determine whether health effects occur and their severity for mercury exposure?

Answer 3

1. The dose
2. The age or developmental stage of the person exposed
3. The duration of exposure
4. The route of exposure

Question 4

Through what process does mercury get into the environment?

Answer 4

Bio accumulation.

Mercury is amplified going up the food chain.

Question 5

What are the natural sources of mercury in the environment?

Answer 5

Mercury occurs naturally in the earth’s crust. It is naturally released from volcanic activity, weathering of rocks.

Possibly the Late-Triassic Extinction - massive volcanic eruption.

Question 6

What is the main main cause of mercury releases?

Answer 6

Human activity - anthropogenic factors.

Coal combustion, mining.

Question 7

How does mercury (Hg) turn into methylmercury?

Answer 7

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.

Heterotrophic microbes break down organic carbon compounds for cellular growth and energy.

Question 8

What is the majority of mercury exposure?

Answer 8

Fish consumption

Question 9

What is the history of understanding the methylation of mercury?

Answer 9

1969: it is possible that living organisms have the capacity to methylate mercury compounds present in pollution (rotten fish, freshwater microbes).
1990s: focus on microbial sulfate reduction in anoxic sediment.
2000s: it is now generally accepted that sulfate reducing bacteria are the key methylators.
2013: identification of genes responsible for methylation are found in many different kinds of microbes.

Question 10

Explain hydro dams and methylmercury.

Answer 10

Dams create artificial lakes, a flooded area. The methyl mercury trapped in the soil is flooded and mobilized - it turns into methylmercury because of the microbes in the water.

Question 11

What are the components of impacts analysis of the Muskrat Falls Dam?

Answer 11

1. Pulse of methylmercury in the flooded reservoir.
2. Transport and accumulation in the downstream environment (Lake Melville).
3. Enrichment of methylmercury in foods (birds, fish, and seals) and changes in Inuit exposures.