Flashcards in Environmental Toxicology Deck (40):
what is environmental toxicology ?
study of the effects of natural and anthropogenic chemicals on communities of organisms and their habitats (ecosystems)
what is our society ?
chemical based society
- advantages to this but there is also down sides such as pollution
what do we do with waste material ?
we have poor management of both risk and environment
- we are not very good at recycline and dispose of chemicals into the environment for dispersal = dilution solution theory
- atmosphere, land, rivers and ocean are viewed as pools for chemical waste to be poured into- however these pools have a finite capacity - therefore accumulation of toxicants can occur and this can be damaging
what can happen to chemicals disposed of in the environment ?
persistance- many chemicals dispersed into the environment dont disappear
degradation- exchange of toxicnt between elements of the biosphere, chemicals can undergo chemical and photo-degradation and biotranformation by microorganisms to more toxic compounds
bioconcentration- toxicants can enter and be concentrated into food chain and therefore animals at the highest trophic level will be at increased risk of harm
biomagnification- build up in food chains- peristant organic pollutants POPs
what chemicals are of particular concern to the environment ?
chemically stable and lipid soluble substances
when does bioconcentration occur ?
when the rate of intake of a chemical is greater than the rate at which an organism can excrete it
what is pollution ?
it is dynamic
- e.g even if you discharge a substance into the air it could be hydrophilic and therefore it can precipitate into rain and concentrate in water
why have the toxic effects of mercury been known about for centuries ?
largely due to the use of mercury, its oxidises and salts for the treatment of syphilis and gonorrhoea
what does the phrase "mad as a hatter" come from ?
the effects of mercury salts on workers using these substances to cure fur felt for the manufacturing of clothes
why has mercury recently become a global environmental pollutant ?
through agricultural use of organomercury fungicides and industrial use of mercury in the production of plastics, paper and batteries
also burning fossil fuels has made significant contributions to mercury emissions in the atmosphere
what influences where a chemical will be discharged into the environment ?
its chemical properties
- whether it will undergo photodegradation
- undergo sedimentation or hydrolysis
- adsorptopn/desorption or biodegradation
- lipid solubility
how many years has mercury been known about ?
at least 2000 years
what are the 3 forms of mercury ?
elemental mercury - Hg0
inorganic mercury- Hg + and Hg 2+
organic mercury- methyl mercury
they are all toxic
elemental and organic are neurotoxic and inorganic primarily damages the kidney
what is cinnabar ?
it is HgS - if you heat it you are left with quick silver which is elemental mercury
what is elemental mercury used for ?
gold mining, scientific instruments and dental amalgams
vapourises at room temp- it is lipid soluble so it readily absorbs through the lungs
it can penetrate the blood brain barrier and can accumulate in the CNS
in cells it is oxidised to Hg 2+ which becomes trapped as it is poorly lipid soluble
what is the main damage caused by elemental mercury ?
damage to CNS- tremor, changes in personality and hallucinations
is the tendency of a chemical to accumulate in living organisms to concentrations in excess of the concentration in its surrounding environment
is the process whereby the concentration of a chemical in an organism is much greater than its surroundings not only due to bioconcentrations but also due uptake from food
what happens when mercury is released into the environment ?
it stays there as it cannot be destroyed so its concentrations increases
- released into environment by coal power stations and claw alkali industry
what is biomethylation ?
it is carried out by microorganisms in both frresh and sea water
- produces alkyl mercury compounds - these compounds readily undergo bioconcentration and biotransformation and this is why fish have the highest levels of mercury mainly present in their muscles
what are mercury salts used as?
fungicides, in fur felting and in some electrochemical equipment
what route is the usual route for exposure to inorganic mercury ?
oral route however bioavailability is poor - only about 7% is absorbed but it is toxic
what is the target for inorganic mercury ?
- causes serious damage to epithelial cells of proximal convulted tubule
- kidney plays key role in excretion of inorganic mercury
- Hg2+ accumulates in the kidney and binds to a group of cysteine rich proteins= metallothioneins - this has a protective role
- at high levels of Hg2+ buffering capacity of metallothioneins is exceeded and toxicity occurs
what are some examples of organic mercury ?
methyl mercury and diethyl mercury
what has organic mercury been used for ?
seed dressings and fungicides
what properties do alkyl mercurials have ?
lipophilic and extremely toxic - leds to neurological damage
how does methyl mercury cross the BBB ?
does it via L-type large amino acid transporter - once they are in the brain they are metabolised to Hg2+ and they accumulate in the CNS as they are charged now and cannot leave
what has happened to the production of mercury ?
production has fallen from 5500-7100 metric tons in 1981 to about 1800 metric tons in 2000
how much mercury is recycled every year ?
what industry in europe was a major user of mercury ?
chlor-alkali industry to produce chlorine gas and sodium chloride from sea water - been a decline in this industry which may release 13000 tons of mercury for recycling
what is mercury used for ?
extraction of gold and silver
scientific equipment- thermometers
what are some examples of mercury salts and what are they used for ?
calomel(Hg2Cl2)- used as a laxative, de-wormer, teething powder and beauty creams
HgCl2- antiseptic, disinfectant and wood preservative
what is the main target organ for mercury salts ?
- little of them are absorbed by GIT however repeated exposure leads to sufficient inorganic mercury to be absorbed = nephrotoxicity
- targets epithelial cells in the renal tubule and accumulates and this can lead to cell death
what is a classic environemental disaster associated with mercury ?
methyl mercury poisoning at minamata bay
how many people were affected by the minanmata diease ?
12000 people and about 1500 people died
how did the minamata disaster happen ?
caused by the discharge of poisonous effluent into the sea at minamata bay by chemical company chisso producing chloride and ethanal
- started around 1930s but the effects were not apparent until 1950s
- they discharged 20-30 tons of mercury into the bay and this led to bioconcentration and biomagnification in the fish and it accumulated in the sediment
what happened within the sediment at minamata bay ?
mercury was converted to methyl and dimethyl mercury by microorganisms
- these alkyl mercurials are lipophilic and enter the food chain causing bioconcentration and biomagnification
- local families and fisherman were poisoned by fish
what were the symptoms of the poisoning at minamata bay ?
difficulty in speaking clearly
constricted visual field
loss of muscle co-ordination
severe cases= cerebral palsy
how does methyl mercury cause neurotoxicity ?
it accumulates in the brain and binds to most subcellular organelles
- it can covalently interact with proteins which contain SH group - this inhibits the activity of many enzymes disrupting cellular processes