Toxicology of Aquatic Contaminants

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Questions and Answers

Which toxin is known to bioaccumulate primarily due to its long half-life?

Arsenic

PCBs (correct)

Dioxin

Methylmercury (correct)

What is the primary way fish absorb mercury from their environment?

In water being expelled through their gills (correct)

Through ingestion of contaminated prey (correct)

Direct absorption from soil

Absorption through skin exposure

Which of the following contaminants is primarily associated with insecticide use?

Mirex

PCBs

PFAS

Toxaphene (correct)

What makes certain PCBs particularly harmful to aquatic ecosystems?

Their chemical stability and retention in the environment Signup and view all the answers

Which metal is found in fish tissue but infrequently at concerning levels?

Selenium Signup and view all the answers

What common household items may contain PFAS?

Water-resistant cookware Signup and view all the answers

Which of the following substances is primarily released as a by-product of industrial processes?

Dioxins and Furans Signup and view all the answers

What distinguishes dioxin-like PCBs from other PCBs?

Their similarity in harmful properties to dioxins Signup and view all the answers

What is a characteristic of ciguatoxin?

It accumulates in the skin and viscera of large reef fish. Signup and view all the answers

Which fish-borne illness is most commonly associated with ciguatoxin?

Ciguatera Signup and view all the answers

What method is involved in the metabolism of ciguatoxin more than 24 hours after exposure?

Phase II metabolism via CYP4 family members. Signup and view all the answers

What is the primary source of saxitoxin?

Phytoplankton that produce toxins. Signup and view all the answers

Which of the following statements about tetrodotoxin is true?

It is lethal at doses between 1-4 mg. Signup and view all the answers

Which seafood product is associated with saxitoxin?

Oysters Signup and view all the answers

Which of the following toxins is known to cause cardiovascular and respiratory failure?

Tetrodotoxin Signup and view all the answers

What is a common feature of seafood toxins like ciguatoxin and saxitoxin?

Both are heat stable and do not degrade during cooking. Signup and view all the answers

What effect does ciguatoxin have on nerve signal propagation?

It enhances depolarization and delays recovery. Signup and view all the answers

Which toxins are known to prevent depolarization?

Saxitoxin and Tetrodotoxin. Signup and view all the answers

What is known about the metabolism of saxitoxin in mammals?

It is not metabolized and remains intact. Signup and view all the answers

What characterizes the metabolism of tetrodotoxin in humans?

The metabolism pathway is still undetermined. Signup and view all the answers

Which factor does NOT favor xenobiotic bioaccumulation in fish?

Low body fat. Signup and view all the answers

What property of toxins makes them easily absorbed from water or diet?

High bioavailability. Signup and view all the answers

Which enzymes are involved in Phase I metabolism of ciguatoxin?

CYP3A4 and various CYP2 family members. Signup and view all the answers

What is a significant characteristic of the toxins mentioned?

They are resistant to metabolic degradation. Signup and view all the answers

Which of the following describes a potential effect of tetrodotoxin consumption?

Sensory disturbances such as hyperesthesia and paresis. Signup and view all the answers

What mechanism primarily initiates the generation of an action potential in neurons?

Opening of voltage-gated sodium ion channels. Signup and view all the answers

What is a possible gastrointestinal symptom associated with seafood toxins?

Nausea and vomiting. Signup and view all the answers

Which of the following symptoms can result from respiratory failure due to tetrodotoxin?

Paralysis of the diaphragm. Signup and view all the answers

What characteristic does ciguatoxin have in comparison to tetrodotoxin?

Ciguatoxin causes longer-lasting symptoms. Signup and view all the answers

What happens to potassium ions (K+) during the action potential process?

They leave the neuron to help repolarize the membrane. Signup and view all the answers

Which of the following effects is associated with hypotension as a result of seafood toxins?

Decreased blood flow to the brain. Signup and view all the answers

Which of the following best explains the concept of bioaccumulation in relation to tetrodotoxin?

It refers to the accumulation of toxins in an organism over time through the food chain. Signup and view all the answers

What is the primary way methyl-mercury is taken up by fish?

By diet or across gills Signup and view all the answers

How does methyl-mercury affect fetal cognitive development compared to adults?

Fetuses are more susceptible, showing effects at 1/5 of the adult exposure level Signup and view all the answers

What is Mirex primarily used for in the southern United States?

As a pesticide Signup and view all the answers

Which toxic substance is known to bioaccumulate significantly in high-fat fish in Lake Ontario?

Dioxins Signup and view all the answers

What characterizes methyl-mercury in terms of its stability and accumulation in the body?

It is lipophilic, resistant to degradation, and bioaccumulates Signup and view all the answers

What is the suspected health effect of exposure to PCBs at lower levels during fetal development?

Impaired cognitive development Signup and view all the answers

What is the estimated half-life of methyl-mercury in humans?

30 to 120 days Signup and view all the answers

Which of the following statements about dioxins is true?

Dioxins exist as byproducts of various industrial processes Signup and view all the answers

What factors influence the recommended restrictions on fish consumption due to mercury exposure?

The health status and age group of the consumers Signup and view all the answers

What is one of the main health effects of methyl-mercury exposure in adults?

Visual, hearing, and other sensory problems Signup and view all the answers

What is the most toxic variation of dioxins mentioned?

2,3,7,8-terachlorodibenzo-p-dioxin (TCDD) Signup and view all the answers

What is the standard average weight used to define a meal of fish in the consumption guidelines?

227 grams (8 ounces) Signup and view all the answers

Which health issue can large exposure to PCBs cause in adults?

Chloracne Signup and view all the answers

During pregnancy, how does methyl-mercury impact maternal and fetal health?

It is stored in maternal fat and can be mobilized to the fetus Signup and view all the answers

Which of the following metals is found in fish tissue but only occasionally at levels requiring restrictions?

Lead Signup and view all the answers

What is the average content of PCBs in Lake Ontario fish compared to the safety limit?

30-fold Signup and view all the answers

Study Notes

Toxic Factors in Fish Products

Unit 9 of NUTR*4510 covers toxic factors in fish products.
Captain Cook's voyages documented early cases of fish poisoning.
His observations likely represent ciguatera and tetrodotoxin poisoning.
Toxins in seafood accumulate up the food chain.

Seafood Toxins

Ciguatoxin:
- Produced by phytoplankton around reefs.
- Bioaccumulates in reef fish (e.g., barracuda, grouper).
- Lipid-soluble and heat-stable.
- Causes ciguatera, a common fish-borne illness.
- Phase I metabolism through CYP3A4 and CYP2 family members.
- Phase II metabolism through glutathione conjugation.
Saxitoxin:
- Produced by dinoflagellates.
- Bioconcentrated by bivalve mollusks (e.g., mussels, clams).
- Water-soluble and heat-stable.
- Causes Paralytic Shellfish Poisoning.
- Not metabolized in mammals.
Tetrodotoxin:
- Origin unknown, likely produced by bacteria.
- Found in puffer fish, blue-ringed octopus, some newts, and frogs.
- Water-soluble and heat-stable.
- Causes "puffer fish poisoning," characterized by rapid onset of cardiovascular and respiratory failure.
- Metabolism pathway in humans is unknown.

Toxicity and Neurological Effects

Seafood toxins cause similar adverse health effects, but differ in their time course of action.
Symptoms:
- Hyperesthesia (increased sensitivity to stimulation)
- Paresthesia (tingling, numbness)
- Sensation of floating
- Headache
- Ataxia (poor muscle control)
- Vertigo
- Respiratory failure (in severe cases)
- Cardiovascular effects (e.g., hypotension)
- Gastrointestinal effects (e.g., abdominal pain, diarrhea, vomiting)

Action Potentials

Nerve signals are triggered by electrical signals that travel along a neuron (action potential).
Depolarization involves ions flowing into the neuron.
Repolarization involves ions flowing out of the neuron.
Ciguatoxin prevents further nerve signal propagation.
Saxitoxin and tetrodotoxin prevent depolarization.

Metabolism of Fish Toxins

Ciguatoxin: Metabolized via CYP3A4 and CYP2 enzymes with phase I and phase II reactions.
Saxitoxin: Not metabolized in mammals.
Tetrodotoxin: Metabolism in humans is unknown, differing from marine species.

Sport Fish Toxins and Xenobiotics (Local Freshwater Fish)

Characteristics of toxins:
- Lipophilic.
- Chemically and metabolically stable.
- Good bioavailability.
- Low toxicity to intermediate food-chain levels.
Conditions favoring bioaccumulation:
- Proximity to contamination sites.
- Increasing age (larger size).
- Diet (favoring larger prey).
- Lipid content.

Common Sport Fish Toxins in the Great Lakes

Main toxins in sport fish include PCBs, Mercury, Toxaphene, Chlordane and Dioxins.
These toxins have long half-lives, resist degradation.

Common Contaminants Monitored in Ontario Fresh Water Fish

Mercury: Converted to methylmercury, bioaccumulates in fish higher up the food chain.
PCBs (Polychlorinated Biphenyls): Persistent organic pollutants; accumulate in fish tissues.
Dioxins/Furans: Unintentional byproducts of industrial processes; very persistent, harmful.
Toxaphene: Persistent insecticide (regulated).
Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS): Don't break down easily.
Selenium, Arsenic, PolyBrominated Diphenyl Ethers (PBDEs), Polychlorinated Naphthalenes (PCNs), Chromium, Mirex, Lead, Cadmium: Other common contaminants in fish.

Bioaccumulation up the Food Chain

Pollutants accumulate in fish at higher trophic levels through the food chain.

Toxins in Sport Fish/Great Lakes Fish Species

PCBs: Problematic due to variations, lingering effects, strong bioaccumulation in high-fat fish. Affects multiple bodily systems.
Dioxins: Extremely toxic, many variations. Bioaccumulate in high-fat fish; persistent effects on health, especially development.
Methylmercury: Mercury is converted to methylmercury by bacteria in the water. Bioaccumulates greatly in high-fat fish, extremely damaging to nervous systems and development of fetuses.

PCBs in Whole Fish

PCBs concentration in fish are decreasing due to regulations.

Guide to Eating Ontario Fish

Provides consumption advisories based on contaminant levels in different fish species, sizes and locations.
Provides the "meal size" for consumption advisories.

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Description

Test your knowledge on aquatic toxins and their effects on marine life. This quiz covers various contaminants, their sources, and their impact on ecosystems, focusing on mercury, PCBs, and ciguatoxin. Dive into this challenging quiz to learn more about what's affecting our waters.