Env toxicology - lists

Important groups of chemicals

Important groups of chemicals

1. metals and metalloids

2. polycyclic aromatic hydrocarbons

3. organo halogenated compounds

4. pesticides

5. other

Chemical properties of polyhalogenated compounds

• Extremely low water solubility
• High lipophilicity
• High affinity to soil organic matter
• High affinity to fatty tissues
• High persistency
Note: PFAS (polyfluorinated compounds) more water soluble, not fat-
accumulating, but extremely persistent

Toxicological properties of polyhalogenated compounds

• Strong bioaccumulation
• Strong food chain accumulation (biomagnification)
• Low acute toxicity (but e.g., acne by dioxins)
• Immunotoxicity (PCBs)
• Estrogenic activity (PCBs, dioxins, DDT)
• Carcinogenicity (dioxins)
• Effects on vitamin A status (PCBs)
• Effects on vitamin K/blood coagulation (PCBs, dioxins)
• Teratogenic effects (dioxins)

sources of PAH

1. crude oil and petrol

2. exhaust of motorized engines

3. burning of organic material

4. industrial sources

sources of dioxins and dibenzofurans

1. Accidents in industries using
chlorinated phenols, e.g., Seveso 1976
2. Impurities (by-products) in chlorinated
pesticides, e.g., 2,4,5-T, Agent Orange
3. Impurities of PCBs
4. Burning of waste materials containing
chlorinated products or chlorine salts
(PVC, pesticide residues etc.)
5. Burning of (salt) peat
6. Effluents of paper mills (chlorine used to bleach paper

important pesticides

1. Chlorinated pesticides
2. Organophosphates
3. Carbamates
4. Pyrethroids
5. Neonicotinoids
6. Phenoxy herbicides
7. Triazines
8. Triazole fungicides
9. Organotin compounds

Degradation of chemicals

1. Decomposition (mainly used in ecology: leaf litter and other
organic material)
2. Photodegradation: by light (visible light, UV)
3. Thermal degradation: by high temperature
4. Chemical degradation: under influence of chemical activity
5. Biodegradation: by the action of microorganisms
6. Biotransformation: inside organisms (to facilitate excretion)
by: 1. Mineralisation à CO2, H 2O, etc.
2. Transformation à metabolites, intermediates

Physical aspects of bioavailability in soil

• Possibilities to penetrate soil
• Rooting depth of plants
• Living layer of soil animals or microorganisms
• Distribution of pollutant over soil solid phase (soil particles) and pore water
• Distribution of pollutant over small and large soil pores
*These factors will determine whether an organism will be exposed to a pollutant or not

Exposure scenario + things to consider

1. subpopulation

2. exposure pathway

3. concentrations and amounts

time unit, allometric unit, temporal scale & endpoint

Mechanisms to reduce toxicity of chemicals

1. Remove chemicals from body
• Passive or active excretion
2. Convert chemical into less toxic form
• Biotransformation, may also facilitate excretion
3. Store chemical in inert form
• Storage of metals in granules or bones
• Storage of organic chemicals in lipids

general principle of biotransformation

1. chemical is converted into polar metabolite

2. molecular weight is increased by conjugation, increasing solubility by transferases

3. excretion is stimulated

general principles of toxicity

1. routes of exposure

2. phases in toxic response

3. endpoints (structural or functional)

4. classification of toxic response

Response to a toxicant depends on

1. type of toxicant & testing organism

2. response type & endpoint

3. exposure duration & environmental conditions

to consider for ecotoxicity testing

1. representative of ecosystem to protect

2. representative of the relevant responses

3. uniformity

4. financial and ethical considerations

Properties of dioxinlike compounds

 Very persistent against breakdown
 Bioaccumulative (hydrophobic)
 Same mode of action
 Same clinical symptoms
 Toxicity is additive: can be summed together

pesticides MoA

• organochlorine pesticides; mess with action potential

• organophosphate esters and carbamatic esters; Ah enzym blockation

• pyrethroids; negative after-potential

• neonicotinoids; activate AhR

Endocrine disrupting compounds

• thyroid hormone disrupting compounds

• steroidogenesis disruption

• estrogen receptor agonists

advantages of biomarkers

1. Integrated measurement of exposure (in space and time)

2. Provide indication of bioavailability

3. Provide some indication of potential risk

4. May provide some indication of route of exposure

5. Can be applied to feral organisms exposed in situ
   • i.e. not artificially exposed

problems with biomarker and interpretation

1. Effect of confounding factors (e.g. temperature, soil moisture, reproductive cycle, life stage, etc.)

2. Statistical vs. ecological relevance of measured response (what is normal level of response?)

3. Meaning of biomarker response for higher levels of biological organization (individual, population, community

4. Specificity vs. non-specificity of biomarker response

biomarker examples

• biotransformation enzymes

• reproductive and endocrine parameters

• neuromuscular parameters

• genotoxic parameters

main assumptions in ecotoxico R.A.

1. Functioning of the system is protected when structure (= species) is protected
2. Sensitivity of ecosystem is determined by its most sensitive species
3. Sensitivity of species in ecosystem can be described by log-logistic or other statistical distribution
4. Maximum acceptable risk (MAR) corresponds to protection of 95% of the species
5. Serious danger (SD) corresponds to protection of 50% of the species

restrictions to SSD R.A.

1. only applicable to toxicity data of same type

2. 8 values needed

3. test organisms should be representative

4. only applicable to species

steps to make a RE framework

1. identify stress and ecosystem process

2. identify response traits to stress

3. identify trophic effect and response traits

4. identify effect traits that determine process

5. analyze linkages between response and effect traits

6. structural equation modelling

problems with RE framework

1. multitrophic environment effects

2. increasing number of trophic levels

3. feedback ecosystem to trophic levels

4. mutualistic interactions underlying effects

pop exposure

1. natural origin

2. intentional poisoning

3. disaster

4. illegal activities

5. background levels

advantage and disadvantages of effect-based monitoring

• acounts for bioavailability and mixture effects

• metabolites and unkown substances included

• cost-effective

- no regulatory threshold

- low substance specificity

- no chronic effect included

- no biomagnification uncluded