Biomagnification, Bioaccumulation, and Environmental Toxicants Flashcards
Ecotoxicology
study of the fate and effects of toxicants in an ecosystem
-distribution, degradation, eventual fate
matrices
atmosphere, lithosphere, hydrosphere, biosphere
Bioavailability
portion of a toxicant that can potentially be taken up by an organism
Bioaccumulation
concentration in an organism is higher than the concentration in the environment via absorption and ingestion
Bioconcentration
bioaccumulation by absorption only
Bioconcentration factor (BCF)
toxicant concentration in the whole organism or tissue to its concentration in the surrounding environment
-hydrophobic compounds
BCF less than 1
toxicant is actively excluded by the organism
BCF=1
toxicant exhibits no selectivity
BCF greater than 1
toxicant is accumulated within organism at higher quantity than in environment
Biomagnification
chemicals become increasingly concentrated at successively high trophic levels
-ratio of steady-state pollutant concentration in the organism
Trophic dilution
concentrations decrease with increasing trophic level
-rates of contaminant biotransformation and elimination exceed rates of ingestion and assimilation
breakdown in environment
-photolysis
-oxidation
-hydrolysis
(POPs don’t readily do the above 3)
-microbial metabolism
photolysis
high energy photons absorbed by a molecule resulting in the breaking or rearrangement of a covalent bond
oxidation
addition of oxygen
hydrolysis
- addition of water molecule
- common in aquatic systems
Microbial metabolism
- microbes have metabolism mechanisms that are not found in eukaryotic organisms
- non-halogenated pollutants can be broken down fairly rapidly
- dehalogenase enzymes can remove the chlorines form POPs and use remaining carbon backbone as a carbon source
- very slow process, only switch on these genes when they are starving
- occurs more readily in soil, POPs accumulate in the hydrosphere
Dirty Dozen
- banned or being phased out due to the Stockholm Convention of 2001
- Came into effect May 2004
- Very persistent in the environment and many are endocrine disruptors
- DDT and PCBs
Polyhalogenated Aromatic Hydrocarbons
- PCB, PCDD, PCDF
- Highly lipophilic, non-volatile, slow to break down, prone to biomagnification, potential for additive interactions
- Halogens bonded covalently to carbon are rare in nature, more difficult to deal with
Polychlorinated Biphenyls
- Class of compounds
- Slightly different chemical structures called isomers and congeners
- Toxic response depends on the properties of the chemical
- thermal stability, low flammability, low vapour pressure, low acute toxicity, but chronic health effects
- halogenation position affects toxicity (3rd or 4th most)
- Must combine with a specific receptor to initiate a reaction which leads to toxic effects
PCB numbering
- ring with fewest chlorines gets the dash
- 1 is always bonded carbon
- Ortho=next to the bond
- Meta=one over from the bond
- Para=across from the bond
- Multi-ortho congeners more likely to be coplanar and less toxic
- 2 in para position is most toxic
Controllable closed systems
- incentive for recovery and ultimate disposal of material used
- coolant in power transformers
- not in direct contact with the environment
Non-controllable closed systems
- recovery and ultimate disposal of material is not monitored
- hydraulic fluids and lubricants
- in direct contact with environment
Open systems
- limited use results in direct environmental contamination when used
- plasticizers agents in paints, adhesives, inks and copying paper
Environmental contamination by PCBS
- open burning and incomplete combustion of PCB-containing solid waste
- Vaporization from open system applications
- Accidental spills or leakages from closed system applications
- Disposal of waste into sewage systems
PCBs acute toxicity
-class 3: moderately toxic
PCBs chronic toxicity
- occupational exposure
- chloracne-acne like skin condition caused by certain toxic chemicals
- swallowing, inhaling, touching chemical
- nausea, vomiting, fatigue vitamin A depletion, liver damage, hormonal changes, lung and live carcinogenicitiy
Yusho Incident
- contaminated rice oil from leaking heat exchanger at a factory in Japan
- Birds died
Yu-Cheng Incident
- contaminated cooking oil
- severe acne, skin pigmentation, conjunctivitis
Endocrine signalling-thyroid hormones
- hormone is made in one area of the body, released into the blood stream, signal is received by another cell in the body, response in the cell
- thyroid gland hormones increase metabolism
- Thyroxine (T4) and triiodothyronine (T3)
- Thyroid glands can absorb iodine
PCBs alter thyroid signalling
- reducing serum levels of T4
- directly activating the thyroid hormone receptors in developing infants
Reducing serum levels of T4
- organochlorines activate phase II enzymes, glucuronidate T4, lead to its excretion via the kidneys
- competition for binding with the serum proteins that carry T3 and T4, less T3 and T4 circulating in the body
Directly activating the thyroid hormone receptors in developing infants
- reduce birth weigh and poor IQ scores
- activate the development of oligodendrocytes (produce myelin sheathes) in tissue culture
- having more oligodendrocytes early in development leads them to die off by apoptosis, less around and neuron development is impaired
PCDDs
- 2 benzenes attached via 2 oxygen atoms
- TCDD most toxic, used in agent orange
PCDD numbering
- first chlorine is numbered 1, then counts up
- Want to number with the most chlorines first
PCDD production
- not produced intentionally
- formed when PCBs are subjected to heat
- combustion of waste with organic waste in presence of inorganic chloride
- by-product of wood pulp bleaching
- manufacturing other chlorinated aromatics
PCDD sources
- processes involving chlorine
- higher the reaction temperature, greater the amount of dioxins produced
- pulp and paper industry
TCDD remediation
- alternatives to chlorine bleach
- elemental chlorine replaced by chlorine dioxide
- use of alternative chemicals: oxygen or ozone
- enzymes used by wood-eating insects and bacteria
- addition of catalysts to reduce need for delignifiers
PDCC sources (2nd set)
- present in the combusted material and not destroyed during combustion process
- organochlorine precursors are present
- high-temperature reaction between non chlorinated organic molecules and chlorine ions
- dioxines have been present at least since anthropogenic combustion of coal and wood commenced
- present in cows milk (high accumulation)
- present in breast milk of women that eat more fats and proteins
Toxicity comparison
- TCDD is among the most toxic anthropogenic compounds
- use it as a reference for toxicity of others
- relative toxicity using LD50 values
Long term effects of dioxin poisoning
- not directly mutagenic
- bind to the aryl hydrocarbon receptor
- transcription factor protein
- moves into the nucleus and switches on the transcription of 60 genes
- natural compounds transiently activate this pathway
- because we can’t metabolize POPs this pathway gets activated more than it should
- lead to developmental defects, promote liver cancer, increasing cell division
- transcription factors are proteins that regulate whether a gene will be expressed to make its encoded protein
PAHs
- fused benzene rings (2 or more)
- contain only carbon and hydrogen atoms
- contain only fused benzene rings
- structure leads to toxic affects
PAH produced via combustion
- burning reaction in which a substance combines with gas
- heat and light accompany combustion reactions
- involve oxygen
Complete vs incomplete combustion
- complete has enough oxygen
- incomplete lacks oxygen, free radicals react with each other when temperature cools to form PAHs
Quantity and type of PAH depends on
- amount of oxygen
- combustion temperature
- nature of organic materials
Some types of organic matter combusted
- coal
- tobacco
- cellulose
- polyethylene
- PAH production during grilling is small due to low temperatures
PAH production in USA
- industrial processes
- traffic
- residential combustion and power generation
- incineration
PAH characteristics
- strong UV absorption
- PAHs occur naturally so ample time for microbial adaptation (biodegradation)
- Larger PAH molecules are more lipophilic
TCDD and PAHs
- TCDD induces the synthesis of enzymes (cytochrome P450)
- Catalyses the biotransformation of lipophilic substances such as hormones, fatty acids, and PAHs
- These products are carcinogenic or exhibit other forms of toxicity
- almost all PAHs are suspected to be carcinogenic
Measuring toxic effects from the wild challenges
- Variation in exposures
- Variation in animal genotype
- Complex interactions in food webs
- Complex interactions with environmental factors
- No controls or replication
Simplified simulated ecosystems
-called mesocosms=an intermediate in complexity between lab experiments and entire ecosystems
Benefits:
-controlled ecosystem
-replication
-can measure toxicant bioaccumulation and biomagnification
-can measure subacute effects on organisms
ELA history and legacy
- started in 1968
- federal government cut yearly budget
- government of Manitoba and Ontario kept it going
- 2015 budget restored federal funding
- operated by the international institute for sustainable development
- cited changed in environmental legislation for harmful algal blooms, acid rain, atmospheric mercury emissions
