Chapter 11: Bioaccumulation

Question 1

What is ecotoxicology?

Answer 1

Ecotoxicology is the study of the fate and effects of toxicants in an ecosystem.

Question 2

What is bioavailability?

Answer 2

Bioavailability is the portion of a toxicant that can potentially be absorbed by an organism.

Question 3

What are the four different matrices that toxicants can move between?

Answer 3

The four different matrices are atmosphere, lithosphere, hydrosphere, and biosphere.

Question 4

What are point sources of pollution?

Answer 4

Point sources of pollution are from a discrete source, such as discharge pipes or effluent.

Question 5

What is the difference between bioaccumulation and bioconcentration?

Answer 5

Bioaccumulation is when concentration in an organism is higher than the concentration in the environment by absorption AND ingestion, while bioconcentration is when concentration in an organism is higher than the concentration in the environment by absorption only.

Question 6

What is BCF, and what does it tell us about the accumulation of toxicants in organisms?

Answer 6

BCF stands for bioconcentration factor, and it tells us whether a toxicant is actively excluded, exhibits no selectivity, or is accumulated within an organism at a higher quantity than in the environment.

Question 7

What is the definition of biomagnification?

Answer 7

Biomagnification is the process in which some toxicants become increasingly concentrated at successively higher trophic levels, via predators feeding on prey items.

Question 8

What is the definition of trophic dilution?

Answer 8

Trophic dilution, also known as biodilution, is the opposite of biomagnification. It occurs when concentrations of toxicants decrease with increasing trophic level.

Question 9

What are the four ways that toxicants can break down in the environment?

Answer 9

The four ways that toxicants can break down in the environment are photolysis, oxidation, hydrolysis, and microbial metabolism.

Question 10

What is the chemical structure of persistent organic pollutants (POPs)?

Answer 10

Persistent organic pollutants (POPs) have a chemical structure that makes them resistant to breakdown by photolysis, oxidation, and hydrolysis.

Question 11

What are some characteristics of PHAHs?

Answer 11

Some characteristics of PHAHs (polychlorinated and polybrominated aromatic hydrocarbons) include high lipophilicity, slow breakdown in the environment, potential for biomagnification, and potential interactions with other toxicants.

Question 12

What are PHAHs and how are they formed?

Answer 12

PHAHs (Polyhalogenated Aromatic Hydrocarbons) are important toxicants that have bicyclic aromatic rings. They are generally formed as products of a reaction between organics and chlorine or other halogens (Br, Fl).

Question 13

What makes molecules containing halogens difficult to metabolize?

Answer 13

Halogens bonded covalently to carbon are relatively rare in nature, which makes molecules containing them more difficult to metabolize.

Question 14

How many kinds of Polychlorinated Biphenyls (PCBs) are there and what are they called?

Answer 14

There are 209 different kinds of PCBs, and they are called different “isomers” and “congeners”.

Question 15

What is the most toxic form of PCBs?

Answer 15

The most toxic forms of PCBs are highly effective at binding at cellular target sites and are resistant to detoxification mechanisms.

Question 16

What led to the wide use of PCBs in the past?

Answer 16

High thermal stability led to the wide use of PCBs in transformers and capacitors, as heat transfer fluids, plasticizers, adhesives, lubricants, flame retardants, and extenders or diluents of other agents.

Question 17

What are some ways that environmental contamination by PCBs can occur?

Answer 17

Environmental contamination by PCBs can result from open burning and incomplete combustion of PCB-containing solid waste, vaporization from open system applications, accidental spills or leakages from closed system applications, and disposal of waste into sewage systems.

Question 18

What is the estimated amount of PCBs in the environment, and where are they distributed?

Answer 18

There is an estimate of about 400,000 tons of PCBs in the environment, with 60% in the hydrosphere, 39% in the terrestrial system, and 1% in the atmosphere.

Question 19

What is chloracne, and what causes it?

Answer 19

Chloracne is an acne-like skin condition caused by certain toxic chemicals including PCBs and PCDDs. It develops a few months after swallowing, inhaling, or touching the responsible agent.

Question 20

What are some symptoms of exposure to PCBs?

Answer 20

Symptoms of exposure to PCBs can include nausea, vomiting, fatigue, vitamin A depletion, liver damage, hormonal changes (thyroidal effects), and lung and liver carcinogenicity.

Question 21

What is endocrine signaling?

Answer 21

Endocrine signaling is when a hormone is made in one area of the body, is released into the blood stream, and the signal is received by another cell in the body.

Question 22

What hormones are released by the thyroid gland?

Answer 22

The thyroid gland releases thyroid hormones [thyroxine (T4) and triiodothyronine (T3)].

Question 23

What is the function of T3 and T4 hormones?

Answer 23

T3 and T4 hormones signal to other cells to increase metabolism among other things. T3 is the more potent hormone.

Question 24

What is the role of thyroid hormones in neurological development?

Answer 24

Thyroid hormones are involved in neurological development in utero and during early childhood.

Question 25

How can PCBs reduce serum levels of T4?

Answer 25

PCBs can activate phase II enzymes that biotransform T4 and lead to its excretion via the kidneys, reducing serum levels of T4 in the body.

Question 26

How can PCBs indirectly affect levels of T3 and T4 in the body?

Answer 26

PCBs can compete with T3 and T4 for binding with serum proteins, such as transthyretin, which can result in less T3 and T4 circulating in the body.

Question 27

How can PCBs directly affect thyroid signaling in developing infants?

Answer 27

PCBs can activate the thyroid hormone receptors in developing infants, which has been linked to reduced birth weight and lower IQ scores in epidemiology and rat studies. Recent studies also show that PCBs activate the development of oligodendrocytes in tissue culture, which are cells that produce myelin sheaths that surround neurons.

Question 28

What is PCDD, and how is it produced?

Answer 28

PCDD stands for polychlorinated dibenzo-p-dioxin, and it is not produced intentionally except for use in analytical work. It can be formed when PCBs are subjected to heat over long periods, or through the combustion of waste with organic waste in the presence of inorganic chloride, among other ways.

Question 29

How can dioxin and PCB poisoning lead to developmental defects and liver cancer?

Answer 29

Dioxins and PCBs bind to the aryl hydrocarbon receptor, a transcription factor that, once activated, leads to the transcription of around 60 genes, including biotransformation genes. This pathway can be activated more than it should when people are exposed to persistent organic pollutants (POPs), which can lead to developmental defects and may help promote liver cancer through increasing cell division.

Question 30

What are PAHs, and how are they formed?

Answer 30

PAHs stand for polycyclic aromatic hydrocarbons, and they are organic compounds that contain fused benzene rings. They are formed through the combustion of organic materials like coal, tobacco, and cellulose, and the quantity and type of PAHs formed depend on the amount of oxygen present, combustion temperature, and nature of organic materials.

Question 31

What are the benefits of using mesocosms to test the effects of toxicants?

Answer 31

Mesocosms are simplified simulated ecosystems that are used to test the effects of toxicants. The benefits of using mesocosms include having a controlled ecosystem, replication, the ability to measure potential toxicant bioaccumulation and biomagnification, and the ability to measure subchronic effects on organisms like reduced fecundity and changes in trophic levels.

Question 32

What is the ELA, and what is its history and legacy?

Answer 32

The ELA stands for the Experimental Lakes Area, and it was started in 1968. In May 2012, the Federal government at the time cut its $2 million per year budget, but the governments of Ontario and Manitoba kept it going. The 2015 budget restored federal funding, and it is currently operated by the International Institute for Sustainable Development (IISD), making it the IISD-ELA. It has published over a thousand peer-reviewed publications and has been cited in changes in environmental legislation related to harmful algal blooms, acid rain, and atmospheric mercury emissions.