Heavy Metal Pollution

liposolubility synergism solubility bioaccumulation mobility

• most HM are highly liposoluble therefore accumulate in the fatty tissues of living orgs • this can lead to increased concs in higher trophic levels - BIOMAG

• some HM have significantly increased effects when working in conjunction with other pollutants e.g. cadmium and zinc

• most HM are soluble at low pH therefore can be mobilised effectively under acidic conditions • we can manage the effects by managing the pH of the solvent to reduce solubility

inhibition of enzyme function, especially nervous system enzymes

• HM may be stored in fat droplets in living cells so that chronic exposure to small doses may eventually produce toxic concentrations by bioacc

Lead Mercury Cadmium Iron Tin

ANTHROPOGENIC - metal production and processing - coal-fired power stations - chemical industry - used to be vehicle exhausts - pipes and paints NATURAL - crust - volcanoes - forest fires - sea salt spray

Sometimes - the uses of lead that cause pollution are but uses that do not continue, e.g. lead-acid batteries/lead flashing used in building construction - the biggest uses of lead do not necessarily cause pollution because they may not cause the release of lead into the environment

• day to day exposure e.g. industry workers inhale dust or absorb it through skin if it dissolves in sweat • nervous system damage • premature births • learning difficulties • v high doses = liver/kidney failure (only really in industrial accidents) • cancer

• toxic to plants/animals • adsorption and release in sed/soil, accumulates • dissolves in acidic water, polluting water course

• change water pipes • change petrol additives • change electrical solder • remove lead-based paint • phase out fishing weights • alternative shotgun pellets

GOOD WORKING CONDITIONS - facemasks - using water sprays - remote operations

• lead been used to make pipes for >4,500 years • small amounts dissolve into the water = chronic exposure through drinking • lead = 20thC replaced in UK by copper, then so was lead solder which held the pipes together (tin, zinc, copper) • some remain in old buildings • in high risk areas, small amounts of phosphoric acid is added to the water supply, producing an insoluble layer of lead phosphate in the pipes which prevents lead dissolving into the water

• anti-knock agents such as TEL were added to petrol to smooth explosive combustion and reduce engine wear, but this meant lead particulates were released into the atmos creating a public health threat • since 1980s, lead been replaced with other chems such as benzene • some fuels like diesel, LPG, hydrogen and alcohol don’t need lead additives

• lead compounds were added to paint to accelerate drying and increase durability • been phased out in many countries since 1980s • if the painted surfaces are intact, no threat posed. If it is old, dusty and flaky it posed risk especially to children who pick particles up under fingernails and suck fingers • however, removing old paint can be a health risk as dust/vapours produced may be inhaled • chemical paint strippers and hot air guns are safer paint removal methods - no lead dust or vapours produced

• lead has been used to make many products e.g. car batteries, roof flashings, paint and some of these uses are only just being reduced/stopped because of the increasing awareness of lead toxicity

• disposal of mercury-containing items e.g. batteries, fluorescent lights, thermometers • chemical plants that produce chlorine using mercury electrodes • combustion of coal

SEVERITY - liquid Hg = not easily absorbed through skin/gut, although vapours may be absorbed in lungs if they are inhaled - inorganic Hg compounds e.g. mercury oxide are absorbed moderately well in the gut - organic Hg compounds e.g. methyl mercury = absorbed easily through the skin/gut/as vapours if they are inhaled. Liposoluble = pass easily through cell membranes including blood-brain barrier where impacts can be more serious. Can also cross placenta and harm unborn babies. Kidney and nervous system damage

• relatively low toxicity inorganic mercury compounds that enter anaerobic seds in lakes or the sea may be changed into organic compounds (e.g. methyl mercury) by anaerobic microbes • the mercury then bioacc and biomag along food chain, often reaching conc that are much higher than the original env release conc

ALGAE - Hg conc 2 ppb - conc factor from water = x20,000 SMALL FISH - Hg conc = 100 ppb - conc factor from invertebrates = x6.7 - conc factor compared to water = x1,000,000 FISH EATING BIRDS - Hg conc = 4,900 ppb - conc factor from large fish = x7 - conc factor compared to water = 49,000,000

RESTRICTION WITH INCREASED KNOWLEDGE OF EFFECTS - Hg thermometers replaced by alcohol/electronic thermometers - Hg can be removed from effluents by reverse osmosis, or by using activated carbon filters - ion exchange filters - disposal at high pH to reduce solubility

• toxic to plants, wildlife, microorgs • very persistent an bioacc and mag in food chains = widespread impact • persistence = can be transported and affects envs at global level

• incineration of wastes containing cadmium pigments e.g. some plastics and paints • disposal of old nickel-cadmium batteries • drainage water from cadmium and zinc mines (often found together) • manu and eventual disposal of old photovoltaic solar panels may cause pollution. It’s one of the few new uses of cadmium • tobacco smoke