environmental toxicity Flashcards
what are the main issues with environmental toxicology
in environmental a few species such as daphnia, bees, trout and quail are used to determine how millions of species and their inter relationships will pan out over time and space
dose response curves and LD50 are widely used
growing use of modelling techniques based on empirical and molecular approaches
the environment is too complex to model and predict outcomes sufficiently well for decision making
there will be exposure to not one but to many chemicals
what are factors effecting environmental toxicology
severity: the degree to which harm or damage is done (depends on sensitivity of species)
duration: how long the effects lasts for (could be decades or more)
extent: the geographical area over which the effect can be found (global impacts from local releases are possible)
release into the environment (point or multiple sources)
distribution in the environment (in which compartment)
metabolism in the environment (maybe in more than one compartment)
pathway from release to receptor (may involve movement through different compartments)
impact on one or more species (including food chain effects)
impact on an ecosystem process such as nutrient cycles or pH balances)
how is realistic information obtained
experimental systems to try to perform tests in as natural environment as possible
aquatic organisms can be amongst the most sensitive
tiered testing approaches (screening: lab centred and based on mortality, field studies over several years and everything in between)
other sources of information are reports such as UK environmental agency containing information such as contaminated land and water pollution
journals such as ecotoxicology, nature
books such as handbook of ecotoxicology
give some example impacts
organochlorine pesticides such as DDT causes eggshell thinning in some birds and dieldrin causes mortality in many species
metals such as lead (causes neurological problems), cadmium (kidney proximal tubule impacts in birds and mammals) and mercury (neurological ones but depends on chemical form)
how does DDT effect the environment
first use in naples in late 40s vs typhus outbreak
is an organochlorine pesticide
caused declines of birds of prey in USA and UK
causes thinner shells in nests
active compound was DDE, very persistent, fat soluble, accumulates along food chains
global distribution
only a few species very sensitive; especially birds of prey such as eagles and hawks since it accumulates along food chains
long experimental programme established impacts via shell formation
how did dieldrin effect the environment
very toxic, kill many species, not at all specific
fat soluble
persists as HEOD in the environment for many years
accumulates in food chains
killed adult birds of prey, DDT and dieldrin were in use at same time one as a spray the latter as a seed dressing so they interacted at the population level effecting breeding success and adult mortality rates- some species became near extinct in areas where used
recovery of bird of prey populations once DDE effects began to diminish and HEOD no longer entering environment
regulation took many years
how do metals affect the environment
lead:
shotgun pellets; a long lasting problem in aquatic areas, kills birds years later if water levels drop
fishing weights; killed swans in great numbers in the UK
pellets mistaken for grit by birds
cadmium:
accumulates in pelagic seabirds; damages kidneys but birds may be adapted
source still unknown; natrual, older plastics?
mercury:
inorganic; potentially harmless if excreted quickly enough
methyl and phenyl mercury compounds: methyl much more toxic than phenyl, methyl mercury is neurotoxin and may have other effects
sources may be natural (volcanic) as well as industrial e.g extraction of gold and commercial sources
methylmercury likely produced in anaerobic marine sediments
marine fish can accumulate high levels; if this is in animal feed then domesticated animals can die
how do PCBs effect the environment
many isomers (over 200)
is an industrial by-product
high levels in 15,000 seabirds that were found dead in irish sea in 1969
cause never definitively established
birds were moulting and in storm conditions had apparently starved
initiated a large international research programme and PCs were gradually withdrawn from use in electrical and heating appliances worldwide
co planar PCBs were the most toxic (a little dioxin like)
how do dioxins effect the environment
another complex group of chemicals
first came to public notice when a factory in seveso in italy exploded, dioxins were found to be widely distributed in the area
suggested to be very toxic but a weak evidence base only
a complex set of local circumstances involving people as well as wildlife and agricultural animals
led to the establishment of the seveso directive of the EU to prevent industrial accidents, an annex for what constitutes a major accident in relation to the environment
later the directive was revised and the annex on wildlife improved with firmer criteria
the directive deals with large industrial plants not just those that might release dioxins
dioxins are released in everyday activity such as firework displays where plastics are used in the firework casing (mostly PVC) can also be released by PVC fires (eg at recycling plants)
were also present in defoliants used in the vietnam war; blamed for many problems
polybrominated biphenyls
michigan USA
mystery deaths and morbidity in cattle
lead to large economic losses
PBBs similar to PCBs but just with a bromine replacing chlorine
mix up in plant (through bad labelling and illiterate worker) led to an industrial cattle feed line becoming contaminated with PBBs
took years to uncover true sequence of events and regulate appropriately
some farm businesses never recovered for range of reasons
how do organophosphorous compounds effect the environment
pesticides such as parathion and malathion
akin to nerve agents in many respects
can interact with one another and with other pesticides by blocking metabolic pathways
species differences in sensitivity (pink footed geese vs other geese)
less persistent than organochlorines
were often sprayed from the air
were often hand sprayed without protective equipment in asia which led to human deaths in several countries
how do organometals effect environment
tributyltin:
antifouling agent on boats
caused intersex in marine molluscs
complex research programme to establish which groups of boats were involved and which estuaries
the first of the endocrine disruptors; this word is widely used to regulate chemicals
alkyl lead:
widely used in petrol engine cars before 1990s; an anti-knock agent
produced by very few factories
killed several thousands of birds on the mersey estuary
experimental and environmental evidence used to find cause and then monitor improvement
many potential causes had to be whittled down to one
chemical did not behave as expected in environment
puzzle of why mortality event happened when it did
is a neurotoxin (worker mortalities were known), implications for human health in area due to wildfowling and local consumption
how does diclofenac effect the environment
is an anti inflammatory
limited use recommended in humans (short duration dosing regimes)
very cheap in india; used to keep cattle going
residues in carcasses taken up by scavenging vultures
bird kidneys and calcium metabolism more sensitive to diclofenac than mammalian systems, vultures particularly sensitive due to their ecological niche and feeding habitats
millions of vultures died, almost became extinct; human implications;
rabies from increased numbers of feral dogs, social and cultural issues; tower burials became very difficult as scavengers were missing, economic impact ran into 100s millions USD
how are neonicotinoids effect the e
neonicitinoids are an insecticide
standard tests can show effects on bees
regulatory best practice said that insects breed so fast that even if 50% mortality would be recovered in next breeding season
however what if next breeding season is interfered with
gathering field evidence took several years and was preceded by more general concerns about bee health declines and loss of bees from diseases or poor husbandry
mixed responses in different parts of the world to mounting evidence; lab and field evidence needed to be combined
eventually responses in different parts of the world to mounting evidence: lab and field evidence needed to be combined
eventually established that honey bees and bumble bees might well be suffering population level declines across the countryside
now banned in EU and UK
how does acid rain and eutrophication effect the environment
acid rain: sulphur
sulphur dioxide released from large combustion plants such as coal fired power stations
acidification of soil and water
knock on consequences for biodiversity eg in upland areas of the UK
addressed internationally by the UN economic comission for europe
control and monitoring based around the critical loads concept
taking many years to see recovery
eutrophication: nitrogen and phosphorous; more local
can both have agricultural sources
organisms such as some algae develop preferentially; blooms visible from space
contamination of lakes, inland waterways and coastal areas
again, critical load medlling is key
restrictions even on the places houses can be built in order to protect sensitive habitats
