Lecture 4 - RH Flashcards
What are polycyclic aromatic hydrocarbons?
Hydrocarbons produced from combustion of fossil fuels or from oil spills that are very toxic
What are halogenated hydrocarbons?
Hydrocarbons with attached halogens.
What are the structural featuers of halogenated hydrocarbons?
Stable
Unreactive
Viscous liquids
What is the solubility of halogenated hydrocarbons?
Low solubility in water
What industrial uses were polychlorinated biphenyls used for?
Hydraulic fluids
Lubricants
Plasticizers
Fluids for transformers and capacitors
Why was the mass production and use of PCBs banned since the 1970s?
Due to their toxicity and persistence in the environment
How are PCBs taken in by aquatic organisms?
From diet, water, algae, and sediments
How do algae absorb PCBs?
PCBs absorbed to surface. (algae have higher concentration than H2O)
How do aquatic organisms accumulate PCBs from sediments? (What is the assimilation like?)
Either contact or ingestion
How are PCBs taken in by terrestrial organisms? (What is the assimilation like?)
Uptake by birds and mammals from diet (90% assimilation), dermal (not studied) and, inhalation (excellent 100%)
How are PCBs dealt with?
Blood cleared to liver and skeletal muscl -> metabolised -> redistributed to adipose tissue or excreted
How was the PCB problem first discovered?
Environmental samples
Research
How are PCBs hydroxylated?
Liver microsomal mixed function oxidase system (MFO system)
What happens to unmetabolised high chlorine content PCBs?
They are stored in lipids and account for large bioaccumulation.
This is also able to cross the placenta affecting babies
What type of toxins are PCBs?
Cumulative toxins
What are the biological effects of PCBs?
Induction of liver MFO system
Increased liver weight and proliferation of S.E.R
Degradation of steroid hormones amongst many others
Reproductive problems in all animals
What is the effect of PCBs on fish and invertebrates?
Reduced reproductive success
What is the effect of PCBs on birds?
Decreased egg production
Eggshell thinning
Altered secondary sex characteristics
What is the effect of PCBs on mammals?
Altered oestrous cycle
Autoabortion
Teratogenic effects
What are Polychlorinated dibenzodioxins (PCDDs) or dioxins?
Extremely toxic compounds that are formed as unwanted byproducts during synthesis of other compounds
how are PCDDs made?
Combustion of PCBs
Interaction of chlorophenols
Major contaminant in phenoxy herbicides (new process has greatly reduced this contamination)
How are dioxins taken up by the ecosystem?
Bound tightly to soil and taken up by plants
Leaching not a problem
Long half and degraded very slowly by bacteria.
What are the biological effects of dioxins?
teratogenic effects in fish
What Is the toxic agent in chick edema disease?
Excessive fluid in pericardial sac is caused by the toxic agent - 1,2,3,7,8,9 - hexachlorodibenzo-s-dioxin
What is the toxicity of dioxins to mammals?
100% uptake regardless of exposure route
Excretion is slow and toxin is accumulated in the liver to be excreted in faeces
Do dioxins bioaccumulate?
Yes
What are EDCs?
Relatively newly characterized group of toxicants that disrupt endocrine function
They can be either natural or synthetic compounds
What are the classes of EDCs?
Androgens + mimics
Oestrogens + mimics
Selected pesticides and metals
PCBs, PAHs, dioxins, ppharmaceutical products
Phytoetrogens
Where can EDCs be released from?
Domestic sewage
Cattle feedlots and dairy
Agricultural runoff
Industrial effluents
Paper and pulp mills
What is atrazine?
A herbicide that has been banned in Europe but still used in the US and research suggests it is a teratogen in amphibians and causes endocrine dysruption
What are some key hormone systems affected by EDCs?
Thyroid hormones
Sex hormones
What is the action of oestrogenic EDCs?
Mimics natural estrogens and causes feminisation of males reducing fertility.
vitellogin induction in male fishes
Ovotestis formation
Shortening of penis of alligators in Florida everglades
Demasculinisation of frogs
What Is the action of anti-oestrogenic EDCs?
Altered maturation and reproductive effects by antagonising oestrogen activity
What is the action of androgenic EDCs?
Mimics natural androgens causing masculinisation of females.
Development of a pseudopenis in female gastropods
What is the action of anti-androgenic EDCs?
Antagonises androgen activity and has reproductive effects
How do pharmaceuticals influence environment?
Through Sewage
What is the influence of pharmaceuticals in ecotoxicology?
Some pharmaceuticals deliberately target oestrogen synthesis pathways
What is the ecotoxicological study amount done on pharmaceuticals like?
Very sparse due to it being a new emerging field but it is rapidly emerging and is a priority research area
What are some pharmaceuticals that deliberately target the oestrogen synthesis pathway?
tamoxifen (breast cancer treatment)
Hormone replacement therapy (Low dose estrogen to treat symptoms of menopause)
Ethinylestradiol (synthetic oestrogen used for contraceptive pill)
Diethylstilbestrol (synthetic oestrogen used to prevent miscarriage)
Where are detergents sourced from?
Widely used for domestic and industrial purposes as soaps, surfactants, emulsifiers, oil dispersants, pesticide formulations, etc
What is the difference between anionic detergents and cationic detergents?
Anionic detergents contain sulphate, sulfonate, or carboxylate ions whereas anions contain ammonium cations
What is an example of non-ionic detergents?
Alykylphenol ethoxylates
What is nonylphenol?
A commonly used non-ionic alykylphenol ethoxylate detergent. It is released to the environment in industrial effluents.
What is the problem with nonylphenol?
It has a similar structure to the oestrogen molecule and can mimick oestrogen’s effects.
This results in vitellogenin formation in male fish and in turn results in gonad histopathology
What are effluents?
Wastewater discharges containing mixtures of several chemicals
What are common sources of effluents?
Sewage treatment plants (STP)
Waste water treatment plants (WWTP)
Dairy sheds
Industrial discharges
What is bioaccumulation related to?
Rate of uptake and the rate of elimination
Why is lipid solubility important for bioaccumulation?
Affects the rate chemicals are taken up.
Organic toxicants are generally lipid soluble and so they can bioconcentrate
What does bioconcentrate mean?
Process by which chemicals enter organisms from surrounding environment (eg water)
What does bioaccumulation mean?
Includes bioconcentration and accumulation of chemicals from food
What does biomagnification mean?
Includes both bioconcentration and bioaccumulation by which tissue concentrations of chemicals increase through trophic levels
What is the bioconcentration factor?
The ability of an organism to accumulate toxicants from the encironment
What is the formula for the bioconcentration factor?
BCF= Concentration of chemical in tissue/Concentration of chemical in water
*Equilibrium must be reached to calculate this
What is the octanol-water partition coefficient?
The Kow is the chemistry expression of the lipophilicity of a chemical
What is the Kow related to?
The BioConcentration Factor
Why is the Kow evaluated with its log?
To make the numbers workable
What is the LogKow related to?
Log (concentration in octanol/concentration in water)
What does the Kow represent?
The ratio of the concentration of a chemical in octanol compared to the concentration in water in a biphasic system of H2O and octanol.
How are the BCF and the Kow related?
Linear relationship between the log of BCF and Kow
How is bioconcentration measured?
- Expose fish to water
- Monitor concentration in fish tissue with time until equilibrium is reached
- At equilibrium measure concentration in fish then divide this by concentration in water
What 2 factors interact to result in a particular bioconcentration factor?
Rate of uptake (absorption of chemical) given by rA
Rate of elimination or excretion of chemical
given by rE
Why do many substances biomagnify?
Due to substances being poorly excreted and the food pyramid where less individuals eat more of the lower trophic level.
What is the fugacity model?
Most widely used model of chemical absorption and magnification and is the most widely accepted explanation for biomagnification.
Fugacity describes the escape tendency (tendency of chemical to go from one media to another eg. food->fish; air->water)
What is important to consider when looking at xenobiotics?
Xenobiotics need to enter the organism for toxicity so environmental concentration is not as important as amount taken up
What is the fate of xenobiotics in organisms?
Sites of action: interaction with endogenous molecules which results in toxic response
Sites of metabolism: Interaction with enzymes and are usually detoxified
Sites of storage: Stored in an inert state
Site of excretion: Mechanism depends on properties such as lipophilicity
How are xenobiotics taken up by terrestrial animals?
Vertebrates: Alimentary tract, skin, and lungs
Invertebrates: Alimentary canal, cuticle, body wall, trachea, gills
How are xenobiotics taken up by aquatic animals?
Mammals/birds: Alimentary tract
Amphibians: Alimentary tract, skin
Fishes: Almintary tract, gills
Invertebrates: Alimentary tract and respiratory surfaces
What are some locations where toxins are excreted?
Bile
Faeces
Urine
How are xenobiotics metabolised?
Biotransformation may lead to detoxification or activation.
Multistep process: Phase 1 metabolism includes oxidation, reduction and hydrolysis. Phase 2 metabolism involves conjugation
Where in the body does xenobiotic phase 1 metabolism take place?
Smooth ER in liver of vertebrates
Usually produces metabolites containing hydroxyl groups such as Mixed-Function Oxidases (MFOs)
Where in the body does xenobiotic phase 2 metabolism take place?
Cytoplasm or ER
Produces polar products via conjugation
Promotes excretion
What happens to xenobiotics that already contain hydroxyl groups?
They directly undergo phase 2 metabolism
What are Mixed-Function Oxidases?
Versatile group of animal enzymes which metabolise many lipophilic xenobiotics except for large highly halogenated molecules
What does cytochrome P450 do?
It activates the phase 1 pathway via oxidation
What does phase 2 metabolism result in?
Greater polarity
Detoxifying function
Promotes excretion in bile or urine
What is a unwanted but possible outcome of biotransformation of xenobiotics?
Activation and formation of reactive metabolites that have toxic effects
Phase 1 metabolism may result in mutagenic metabolites such as Benzo(a)pyrene
How do plants take in toxicants?
Through stomata although cuticle may be altered.
Gas to diffusion pathway important
May be particles droplets or vapor
What is the pathway for plant injury induced by air pollutants?
Leaf (exposure)-> Epidermis (Uptake)-> Intercellular space (transport)-> Spongy parenchyma (storage) -> Pallisade parenchyma (metabolism) -> Epidermis (excretion)
What is a possible use for plants regarding toxicants?
They can be used to decrease metal toxicants due to their ability to produce lots of metallotheins
What is polarity’s role in pollutant distribution and persistence in aquatic environments?
Hydrophilic compounds tend to dissolve
Lipophilic compounds associate with sedimnets or surface oil films
Pollutants in sediments are limited in mobility and available to benthic organisms
Temperature and pH do influence availability
What happens to pollutants in soil?
They can leach into ground water or they can be taken in by soil organisms to form metabolites
How are ecosystem effects of toxic effluents/contaminated soil monitored?
Lab testing
In situ biomonitoring (Test organisms placed in path of toxicant)
OR
Ecosystem responses can be tested before and after contamination incident
What are the 2 classes of responses of ecosytems to toxicants?
Ecosystem structure
Ecosystem function
What are the possible endpoints for monitoring ecosystem effects?
-Functional endpoints: Rate of biomass production Rate of primary productivity Rate of community respiration Rate of nutrient uptake/regeneration Rate of decomposition Rate of recovery after stress
-Structural endpoints: Species richness Species abundance Similarity Biomass
What are the 4 main approaches to in situ biomonitoring?
- Community/Ecosystem changes
- Measuring concentrations of pollutants in indicator or “sentinel” species
- Assessing biological effects of pollutants on individual organisms and relating these to other biotic and abiotic factors
- Detecting genetic differences that may have evolved in response to a pollutant - changes in genes and gene regulation
How are community effects measured (type 1 monitoring)?
What is present?
How many?
What kind? (sensitive/resistant)
What condition? (Health/reproduction)
What are the 3 approaches to monitoring changes in communities?
Biotic approach: Based on sensitivity of species to pollutants
Diversity approach: Based on changes in diversity
AUSRIVAS: Assessment in terms of species and relative abundance of families present
What is measured regarding ecosystem function?
Changes in system over time through homeostatic mechanisms
Measured as rate of change - growth rate, production rate, transformation rates, transfer rates
What are the characteristics required for a biomonitor?
Should be common and diverse
Relatively sedentary
Accumulate pollutant yet tolerate moderate concentrations
Life-span of months to years
Concentration should not be affected by reproductive cycles or sex differences
Relatively large (adequate biomass for analysis)
Identification should be straightforward
How can you measure organism responses to pollutants?
Primary aim is to understand, describe and predict the effects of pollutants on organisms and ecosystems
Time scale of effects is important
How do organisms become genetically resistant to pollutants?
Evolution
