Contaminants

• Contaminant

  Concentration > natural concentration as a result of human activity, only causes deviations from the normal composition of an environment
• Pollutant


  Concentration > natural concentration as a result of human activity, net detrimental effect upon its environment or upon something of value in that environment
• Microbial contamination of urban rivers is a major health issue
• Microbial and macronutrient status of the River Thames in London

  Has clearly improved over the last 50 years
• In addition to legacy contaminants, there are many emerging concerns: plastics, pharmaceuticals, drugs of abuse, personal care products etc.
• Organic compounds

  All carbon containing compounds except carbonate salts (CO3^2-), carbon oxides (COx) and cyanide (C=N). C, H, O, S, N. Over 20 million known organic compounds, 20 times more than all other known chemicals combined.
• Over 350,000 chemicals have been registered for production and use (19 countries)
• In Aotearoa NZ, there are 150,000 substances approved, less than 200 monitored, and no national record of chemicals imported, used, discharged in the environment

  
• Biological vs chemical contamination of water resources
• Microbial contamination is closely monitored everywhere due to high risk to human health even at low levels
• Chemical contamination is invisible
• The status of rivers in cities has generally improved over the last 50 years, with microbial and macronutrient status clearly improving

  
• A study along the Thames detected 41 pharmaceuticals up to 10 µg/L, 2 lifestyle compounds (cocaine and sucralose), and antimicrobials in all samples downstream of the source
• Organic contaminants


  • Wide range including classical (BTEXs, chlorinated solvents, PCBs) and emerging (PPCPs)
  • Environmental behaviour: partitioning and degradation
  • Impact: toxicity to human and the environment (ecotoxicity)
  • Mitigation and remediation strategies
• Xenobiotics (foreign chemicals) can interact with cells, tissues, organs and cause toxic responses
• Kinetic phase


  Metabolism and excretion, organisms as compartments
• Dynamic phase


  Biochemical effects
• Extrapolation from simplified toxicity tests to complex and diverse exposure patterns in the environment is very challenging
• Aquatic toxicity assessment

  • Base set for industrial chemicals: fish, crustaceans, algae, bacteria
  • Dose-response relationships, LC50, EC50, LOEC, NOEC
  • Toxicity scale for aquatic organisms
• Terrestrial organisms like soil invertebrates, microorganisms, birds and bees are also tested for toxicity, but monitoring is more common than testing
• Effects of chemical mixtures are still poorly understood, with potential for additive, synergistic, potentiation or antagonistic effects
• Demonstrating a direct link between a chemical and a health outcome in humans is very challenging due to confounding factors, long latency, and difficulty in measuring individual exposure
• Toxicity to humans is mostly based on extrapolation from animal toxicity studies for existing and new chemicals
• Antagonism


  An active substance decreases the another active one (1+1=1)
• Effects of mixtures are still poorly understood
• Environment: complex and dynamic mixtures
• How do we know if contaminants are toxic to humans?
• Toxicity to humans


  • Epidemiological studies from occupational/accidental exposure
  • Demonstrating a direct link between a chemical and a health outcome is very challenging (unless extremely high exposure)
  • Mixture of toxicants
  • Long latency, population migration
  • Individual exposure difficult to measure
  • No dose-response relationships
  • Confounding factors (e.g. socio economic status, smoking)
  • Low number of cases, difficulty in showing a significant difference compared to a control population
• Toxicity to humans (for existing and new chemicals)

  • Mutagenicity (Ames test on Salmonella bacteria)
  • Irritancy/sensitization (eye, skin)
  • Teratogenicity (developmental/reproductive)
  • Acute/chronic rat toxicity (LC50 in mg/kg bw)
  • Carcinogenicity
• Exposure, Occurrence of cancer, Slope factor: No safe dose for carcinogenic chemicals!
• Animal testing very controversial as many scientists argue that toxicity cannot be extrapolated across species
• Toxicity scale for human

  Increasing toxicity: Dose of 350 mg for a person weighting 70 kg, Dose of 1 kg for a person weighting 70 kg
• Endocrine disruptors

  Substances that act like hormones in the endocrine system, disruption of endogenous hormones functions
• Endocrine disruptors: Effects include reduced fertility, skewed male/female sex ratios, loss of foetus, early puberty, brain/behaviour problems, impaired immune functions
• Endocrine disruptors: Dose–response controversy: effect at very low concentration not deducible from higher dose, Difficulty in defining some regulatory maximum concentration
• Endocrine disruptors


  • Encompass a variety of chemical classes
• Human exposure to endocrine disruptors: food (PCB, DDT, PBDE), indoor air/dust (PCB, PBDE, Phthalates), water/baby bottle (Bisphenol A)
• Key points

  • Wide range of effects
  • "The dose makes the poison" or "the solution to pollution is dilution" - Concept of dose-response relationship
  • The effects of real exposure patterns (frequency, duration) and mixtures is difficult to predict
• Contaminants move around and distribute
• Ways to group contaminants

  • Chemical structures: systematic nomenclature
  • Compartment: air, water, soil
  • Type of effects: carcinogen, endocrine disruptors
  • Physico-chemical properties (hydrophobic, polar, volatile, persistent)
  • Sources: leaking tanks, incineration, industry, sewage, runoff etc.