12. Contaminants

What are the four steps of risk assesment?

• Hazard identification

• Hazard characterization (dose-response)

• Exposure assessment

• Risk characterization

  • Risk management

  • Risk communication

Unavoidable vs avoidable chemicals

• Contaminants are the unavoidable chemicals

Persistent Organic POllutants (POPs)

• Mostly anthropogenic, persistent carbon-based chemicals that bioaccumulate and are toxic → found everywhere in the environment

• Includes:

  • Organochlorine pesticides

  • Polychlorinated biphenyls

  • Dioxins

  • Brominated flame retardants

  • Perfluoralkylated substances

Persistency, bioaccumulation and toxicity of POPs

• Persistent: do not degrade easily in the environment, typically accumulate in fatty tissues and are only slowly metabolized

• Bioaccumulative: concentrations in organisms accumulate over time

• Toxic: exposure associated with chronic adverse health effects, including cancer and developmental and reproductive toxicity

They are PBTs (persistent, bioaccumulative, toxic)

Biomagnification

• Bioaccumulation up through trophic levels

• Increasing concentration of chemical in tissues of organisms at higher levels in a food chain due to high lipophilicity and persistence (chemicals gather in fat)

Three types of POPs

• Pesticides esp. organochlorine pesticides incl. DDT

  • considerd avoidable chemicals

• Industrial and technical chemicals incl.

  • PCBs (polychlorinated biphenyls)

  • PBDEs (polybrominated diphenylethers)

  • PFAS

• By-products of industrial processes incl

  • PCDDs: dibenzo-p-dioxins

  • PCDFs: polychlorinated dibenzofurans

POPs in our environment

• Halogenation → resistant to degradation → persistent

• Peak release of POPs in 1970s

  • Except PFAS, contaminant of emerging concern (CEC)

• Now ±10% of peak concentrations in environment

  • Travel through air, water - even antartica

How POPs end up in our food

• Over 90% of human exposure to POPs is through the consumption of contaminated food, esp. food of animal origin → fish

• Depostion on crops

• Drinking water

• Soil ingestion by grazing animals

• Bioaccumulation through trophic levels

• Food preparation

• Breastmilk

Agent orange

• Agent orange is a herbicide and defoliant chemical contaminated with TCDD

• Herbicidal warfare programme in vietnam war, 1961-1971

• 3 million people suffered illness

• Developmental defects in children military personnel and inhabitants

Usage of dioxin-like chemicals, PCBs

• polychlorinated biphenyls

• Anthropogenic

• Used as dielectric and coolant fluids in electrical apparatus, carbonless copy paper and in heat transfer fluids until 1979 in US, Stockholm Convention 2001

• 2 categories: non-coplanar (ortho-substituted) congeners vs coplanar congeners ← Dioxin-like

PCB exposure incidence

• Skin because skin is fat

PFAS

Heavy metals

Includes:

• mercury (Hg)

• Lead (Pb)

• Cadmium (Cd)

• Arsenic (As)

• Current exposure levels raise concern for (developmental) neurotoxicity, nephrotoxicity, carcinogenicity

What are metals

Common non-essential metals in food

Why do fish contain mercury?

• Hg²⁺ converted to MeHg by anaerobic microorganisms

• Fish accumulate MeHg in fat tissue

Toxicokinetics of mercury

• Long half-life ±50 days

• Accumulates in liver, kidneys and brain

What is a mycotoxin?

A toxic chemical produced by fungi known to contaminate food and pose health risks to humans and animals

History of myoctoxins

• A public health risk for a long time

• Erogtism: the oldest recognized mycotoxicosis of humans

• Produced by Claviceps purpurea (ergot) fungus on rye

• After periodic outbreaks in central Europe, the disease became epidemic in the middle ages

• Symptomology: gangrene (blackened limbs) due to vasoconstriction of blood vessels in extermities, neurotoxicity (madness)

Why are mycotoxins still a risk

• Expected to increase due to climate change

• They are hard to get rid of, very persistent and processing does not remove or kill them

Aflatoxin

• Produced by Aspergillus flavus and A. parasiticus

• Found on peanuts, soybeans, rice, pepper, corn