Lecture 23-24

Question 1

What is mercury?

Answer 1

Naturally occurring element that is found in air, water and soil

Used in thermometers, barometers, fluorescent, lamps, etc.

Question 2

What is the difference between inorganic and organic mercury?

Answer 2

Inorganic mercury:
- low absorption (0.01-7% avg)
- people become exposed through their occupation (that involved inorganic mercury)

Organic mercury:
- high absorption (>90%)
- primarily a central nervous system toxin
- half-life of 50-70 days
- people may be exposed through their diet (bioaccumulation, biomagnification)

Question 3

What are the health effects of mercury exposure?

Answer 3

Inorganic mercury and methylmercury are toxic to the central and peripheral nervous system
- loss of physical coordination, difficulty in speech, hearing impairment, blindness, death

Children who had been exposed in-utero through their mothers’ ingestion often have motor difficulties, sensory problems and intellectual disability

Factors that determine whether health effects occur and their severity include:
- the dose
- the age or developmental stage of the person exposed
- the duration of exposure
- the route of exposure (inhalation, ingestion, or dermal contact)

Question 4

How does mercury relate to bioaccumulation?

Answer 4

There is more mercury the higher up the trophic levels you go (smaller fish have less mercury)

If the concentration of methylmercury in lake water is considered to have an absolute value of 1, then approximate bioaccumulation factors for microorganisms like phytoplankton are 10^5

Question 5

What is the Minamata Disaster?

Answer 5

Industrial wastewater containing methylmercury from a petrochemical plant was released into Minamata Bay from 1932 to 1968

Caused Minamata disease (neurological syndrome caused by severe mercury poisoning)
- numbness in limbs/lips
- difficulty hearing/seeing
- shaking in arms and legs
- shouting uncontrolloably

Women gave birth to poisoned babies with severe deformities

Question 6

What are the sources of mercury to the environment (naturally)?

Answer 6

Mercury occurs naturally in the Earth’s crust. It is naturally released into the envr from volcanic activity, weathering of rocks (without human input).

Input into ocean/soil as water soluble. Either gets buried and then uplifted through volcanic activity, or reduced in the ocean/soil and released back into the atmosphere

Question 7

How is human activity causing the release of mercury?

Answer 7

Mercury now primarily enters the atmosphere through the combustion of coal/mining

It is extracted from its burial phase and made volatile/water soluble.

Reservoirs have increased due to anthropocentric perturbation

Question 8

How does mercury turn into methylmercury?

Answer 8

Methylmercury is formed from inorganic mercury by the action of bacteria (microbes) 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.

OM (electron donor) + Electron acceptor (e.g. O2, SO4) + inorganic mercury –> microbial cell –> methylmercury

Takes inorganic mercury and attaches a methyl group to turn into methylmercury (attaches a C and 3H)

Question 9

What consists of the majority of mercury exposure ?

Answer 9

Fish consumption

> 90% exposure from marine species

Question 10

Characteristics of sulfate-reducing microbes

Answer 10

Heterotrophs (obtain energy from eating organic compounds)

Live in anaerobic environments (low or no O2)

Use sulfate as an electron acceptor instead of O

It is now generally accepted that sulfate reducing bacteria are the key methylators, however genes responsible for methylation are found in many different kinds of microbes (e.g. methanogens) not just sulfate reducers

Question 11

How does hydroelectricity work?

Answer 11

Hydroelectric power is produced as water passes through a dam and into a river below

The more water that passes through a dam, the more energy is produced

Once a dam is built, an artificial man-made lake is created behind the dam

Electricity is produced by a device called a turbine

Question 12

How do hydrodams impact methylmercury production?

Answer 12

Through flooding of soils, causes a pulse in methylmercury

Before flooding, microbes have exposure to oxygen. However, after flooding, everything upstream of the dam is flooded. Vegetation is submerged in water, causes microbes to methylate mercury since they do not have oxygen (anoxic envr)

Question 13

What are the components of the impacts analysis of the effect of the Muskrat Falls dam project on methylmercury concentrations?

Answer 13

Pulse of methylmercury in the flooded reservoir
- rapid increase in methylmercury in river water above saturated soils 3 days after flooding

Transport and accumulation in the downstream envr (Lake Melville)

Enrichment of methylmercury in foods (birds, fish and seal) and changes in Inuit exposures
- food advisories are the only real mitigation measure in practical use
- however, food is extremely expensive in remote communities –> procuring own food is really the only accessible way to eat

Question 14

What was included in the committee report in April 2018 regarding the Muskrat Falls dam?

Answer 14

Public info campaign

Monitoring program

Negotiate an impact security fund prior to full flooding

Targeted removal of soil and capping of wetlands

Question 15

What are some factors that affect microbial communities?

Answer 15

Temperature
Rainfall/moisture
pH
Salinity
etc…

Question 16

What are the two subcycles of the carbon cycle?

Answer 16

rapid carbon exchange: among living organisms

long-term cycling: geological processes

Question 17

What is the role of microbes in the global carbon cycle?

Answer 17

Biological carbon pump: photosynthetic microorganisms (phytoplankton) drawdown CO2 from the atmosphere during photosynthesis
- inorganic carbon gets pulled down into the ocean turned into organic carbon and 99% respired back out as CO2

Question 18

How does microbial respiration and decomposition lead to the release of CO2?

Answer 18

OM (electron donor) + electron acceptor (O2) –> microbial cell –> CO2

Heretrophic microbes break down organic carbon compounds for cellular growth and energy

Primary way that CO2 gets back into the atmosphere

Question 19

What is organic matter and where does it come from?

Answer 19

Organic matter is material that has come from a recently living organism

It includes the remains of organisms such as plants and animals and their waste products in the envr

Consists of thousands of individual compounds and unrelated substances (polysaccharides, plant waxes, lipids, proteins, lignin, etc.)

Most organic matter is chemically uncharacterizable

OM is one of the largest reservoirs of carbon on the planet (40% of Earth’s organic carbon is stored in sediments in form of OM)
- marine sediments are estimated to contain half of the microbial cells found in the ocean

Question 20

Where is most OM derived from in SOM?

Answer 20

Plants

Question 21

Where is most OM derived from in marine envr?

Answer 21

Phytoplankton (photosynthesizing microscopic organisms. Can be bacteria or eukaryotes)

Question 22

What controls the availability of OM to microbes (bioavailability)?

Answer 22

The fate of OM is primarily determined by the activity of microorganisms
- the only way for microbes at the bottom of the ocean to acquire energy is through OM consumption

Bioavailability is thought to be dictated by intrinsic chemical properties of the compounds (size and structure), but this is not always the case
- ex. lignin molecule is assumed to be resistant to microbial degradation upon release from soils to aquatic settings, however lignin disappeared within days of incubation with Amazon River water

Therefore, the bioavailability of OM is affected by more than just chemical properties

Question 23

Order active OM, slow OM and stable OM in terms of bioavailability, size and structure

Answer 23

Active OM: most bioavailable, low molecular weight and aliphatic (simple structure)

Slow OM: in the middle

Stable OM: least bioavailable, high molecular weight, highly aromatic (more chemically complex)

Question 24

How can we track the source, age and sequence of carbon compounds that are degraded by microorganisms?

Answer 24

Isotopic carbon respirometer bioreactor measures and collects CO2 for carbon isotope analyses

Heterotrophic microbes show similar isotopic signature as carbon source –> “you are what you eat (and breathe) principle”
- we can measure the C13 and C14 ratio signature of respired CO2

We can use carbon isotopes signatures of respired CO2 to estimate the contribution of different types of OM to respiration

Question 25

What is a key step in OM degradation in the ocean?

Answer 25

Extracellular enzyme activity

Microbial calls are small, therefore can only take in compounds that will fit in their portals
- Some microbes will secrete enzymes to break down macromolecule OM

Genomic characteristics are related to the observed patterns of OM degradation
- Ex. pseudoalternomonas spp. was found to have four times more copy numbers of genes encoding for extracellular peptidases (protein-degrading enzymes)

Question 26

What are the two ways in which species-level differences of pseudoalteromonas spp and virbio splentidus impact the rate and total qty of OM degraded ?

Answer 26

Isotopic measurements of respired CO2 show species level selectivity of carbon substrates

OM degradation patterns are consistent with genomic characteristics of these two species

Question 27

How much land area does permafrost cover?

Answer 27

27%

Question 28

How is the warming of the Arctic causing a positive feedback loop?

Answer 28

Ice and snow reflect up to 80% of sun’s radiation

Warmth is causing it to melt, exposing dark water that only reflect 20%

Less ice and snow –> more warming –> less ice and snow

Question 29

What is the impact of thawing permafrost?

Answer 29

Permafrost contains large stores of OM that have been locked for thousands of years
- almost twice as much carbon as is currently contained in the atmosphere is stored in soils/permafrost of high latitude ecosystems

Thawing permafrost will cause microbes to make a shift from dormancy to activity since when the climate warms, microbes become active and degrade OM leading to the release of GHG
- usually, they are seasonally frozen and preserve within permafrost

Most bacteria release CO2 as a byproduct of their metabolism

Some microorganisms can release methane (30x more potent as a heat-trapping gas compared to CO2)

Question 30

Methanogens characteristics

Answer 30

Belong to the archaea group of prokaryotes

Produce methane as a byproduct of their metabolism

They are extremely oxygen sensitive and require anaerobic conditions

Found in the digestive systems of herbivores as well as marshes and aquatic sediments