Toxic Substances

Definition and Concept

• Toxicity: Assessing how harmful substances are to living organisms and ecosystems.

Historical Context of Pollution

Hudson River Pollution

• General Electric Pollution (1947-1977):
  • Dumped over 500,000 kg of waste containing PCBs into the Hudson River in New York.
  • In 2002, the EPA ruled that General Electric must clean up the contamination.
  • General Electric fought this decision in court, leading to a litigation period of seven years.
  • They began clean-up in 2009 and completed it in 2015, incurring costs of $1.6 billion.

Factors Influencing Toxicity

Concentration and Exposure

• To assess the harm of a chemical in the environment, consider the following factors:
  • Persistence of the chemical.
  • Route of exposure.
  • Solubility of the chemical.

Persistence

Understanding Persistence

• Persistence: Refers to how long a chemical remains in the environment without breaking down.
  • Measured by the half-life – the time required for half of the substance to degrade.
  • Factors affecting half-life include:
  • Breakdown by microorganisms.
  • Environmental conditions such as pH, sunlight, and heat.
  • Interaction with other molecules.

Example of Persistence

• Mercury's Interaction: While mercury is usually harmless, it can interact with carbon (C) and hydrogen (H) to form methylmercury ($CH_3Hg^+$), which is highly toxic.

Routes of Exposure

Exposure Pathways

• Chemicals can enter organisms through multiple pathways:
  • Air.
  • Food.
  • Water.
  • Soil.

Solubility

Solubility Characteristics

• Water Solubility: The more soluble a chemical is in water, the more mobile it becomes and the higher the likelihood it enters ground or surface water.
• Oil Solubility: Chemicals soluble in oil tend to remain in soil or accumulate in the cells and tissues of organisms post-exposure.
  • When accumulated, they can be transferred through the food chain.

Worksheets and Questions

Persistence Importance

1. Why is the persistence of a chemical an important factor?
   • c. Pollution by persistent chemicals can pose a risk for decades.

Hypothetical Calculation

2. Determine the concentration in a river after 10 years if a chemical has a half-life of 2 years with an initial concentration of 1,280 g/L:
   • The concentration after 10 years is calculated as follows:
     • After 2 years: $640 ext{ g/L}$
     • After 4 years: $320 ext{ g/L}$
     • After 6 years: $160 ext{ g/L}$
     • After 8 years: $80 ext{ g/L}$
     • After 10 years: $40 ext{ g/L}$

Malaria and DDT Use

Malaria Impact and DDT

• Malaria Statistics: Annually 350 million to 500 million infections with approximately 1 million deaths.
• DDT Offensive (1951): Used extensively in the USA to eradicate malaria.
• Controversy: In the 1960s, the adverse effects of DDT on non-target species, especially birds, were studied, leading to its ban in 1972.

Consequences of DDT

• The chemical's bioaccumulation was detrimental, specifically to predatory birds like bald eagles, which had thinning eggshells due to the chemical's presence in their prey.
• The banning of DDT is linked to the recovery of bald eagle populations in the USA.

Biomagnification and Research Studies

Investigating Bioconcentration

• Research teams evaluate biomagnification through the blood levels of DDT in food web organisms, including primary, secondary, and tertiary consumers.
• Study Focus: Testing for blood concentration levels of DDT and its implication on health across trophic levels.

Hypotheses Formulation

1. Testable Hypothesis: Blood levels of DDT in consumers will increase as the trophic level increases.
2. Dependent Variable: Concentration of DDT ($c$) in the consumers’ blood.

Risk Assessment

Types of Risk Studies

1. Dose-Response Studies: Expose test organisms to varied concentrations of chemicals to observe effects (mortality, behavior, reproduction).
2. Retrospective Studies: Compare health outcomes between exposed and non-exposed populations over time.
   • Notable case: Bhopal Gas Tragedy (1984) resulted in long-term health issues for survivors due to methyl isocyanate exposure.
3. Prospective Studies: Follow a group exposed to a chemical over time and analyze health impacts compared to a control group.

Lethal Dose Studies

• LD50 Curve: Describes the concentration at which 50% of test animals die, providing insight into a chemical's toxicity.
• Comparison with Safety Standards: Environmental agencies commonly set safety levels at 10% of the LD50.
• Human safety levels are significantly stricter, at 0.1% of the LD50.

Risk Analysis Framework

Risk Analysis Steps

1. Risk Assessment:

   • Identify the hazard.
   • Determine the potential harm (dose-response).
   • Assess the probability of exposure.
   • Risk Calculation Formula: $ext{Risk} = ext{Probability of Exposure} imes ext{Probability of Harm}$

2. Risk Acceptance:

   • Define what is an acceptable risk level (e.g., EPA standard of 1 in 1 million).

3. Risk Management:

   • Balance potential harm against social, political, economical, and ethical factors.
   • Example of Arsenic Regulation: A safe concentration was set at 10 ppb, while practical limits were adjusted based on feasibility to maintain drinking water quality.

Philosophies on Risk Management

Approaches to Risk

1. Innocent until Proven Guilty: Products are allowed on the market without comprehensive pre-market testing.
2. Precautionary Principle: Emphasizes thorough research before allowing a product to be sold, which may include years of studies and high costs.

International Conventions and Regulations

Stockholm Convention

• 2001 Agreement: 127 countries agreed to limit the use of 12 endocrine-disrupting chemicals, including DDT and PCB. Updated in 2017.

REACH Initiative

• Established in 2007 by the European Union to regulate chemical safety, mandating manufacturers to prove safety before market release (fully realized by 2018).

Additional Worksheets and Considerations

Risk and Health Statistics

• Comparative statistics on the risk of various health hazards, e.g., heart attack, cancer, car accidents, etc.

Case Studies and Worksheets

• Worksheets to investigate cancer risk probability, benefit implications of the precautionary principle, and designing hypothetical studies to evaluate chemical effects on health.

Concluding Notes

• Research Importance: Understanding chemical harm, pollution persistence, and the effect of regulations is vital for ecological health and human safety.
• The impact of historical and present chemical usage highlights the need for comprehensive risk assessment strategies and regulatory frameworks.