Stressors in the Great Lakes: Heavy Metals

No generally accepted definition exists for heavy metals

Defining factor: 5 g/ cm3

Definition

Heavy Metal in the Great Lakes

Concentrations in the Great Lakes (ppt)

Mercury

Cadmium

Lead

Lake Huron

60 16 38

Lake Superior

98 27 39

Lake Michigan

52 42 260

Lake Erie

42 98 910Bernier et al., 1995

Industrial sources of Heavy Metal emissions include:

Waste oil Solid waste incineration / coal burning and

ash Iron and steel productionSmelting Battery and lead alkyl manufacturingLead-Historically fuels in cars and trucks

(regulations and lead free gasoline)

Sources

ArsenicCommonly occurringHard to measure

direct sourcesUse has decreased

greatly since 1980

Arsenic ToxicityArsenic is used to kill

Insecticides, herbicides, fungicides, preservatives

Arsenic kills by disrupting the cellular process that produces ATP.Blocks and competes with chemicals that form

ATPMakes it difficult for muscles to fireOrgan systems shut down due to lack of energy

1 mg/kg/day is the acute lethal dose50 ppb will lead to precursors for cancer

Transition metal like zinc and mercury (happy in oxidation state of +2)

Rare metal- 0.1 ppm in Earth’s crust most in zinc ores

A byproduct/impurity from zinc production (mining, smelting, refining)

Cadmium

Cadmium Uses Resistant to corrosion-

Used for electroplating of iron

Used as color coating/pigments in paints ( mid 20th century) various salt forms

Carboxylate forms of cadmium (laureates & stearates) for stabilizing PVC

Growing demand for nickel-cadmium batteries in 21st century

Solar cells

Burning of fossil fuels (coal) creation of cadmium oxide (CdO)

High cadmium conc. of phosphate fertilizers from mined rocks into soils

Dissolved by acid to create chlorides, sulfates, and nitrates Reclaimed from iron/steel recycling in dust Solid waste incineration (Milorganite)

Entrance into the Environment

Intake normally through inhalation and ingestion

Absorbed into kidneys Bioaccumulation in marine life No known useful role for Cd in higher

organisms Certain marine diatoms in low zinc conc.

Utilize Cd for carbonic anhydrases

Cd Transportation & Fate

Metal fume fever- Inhalation of certain metal oxides (flu like symptoms

Compounds containing Cd are carcinogenic Inhalation leads to respiratory and kidney

issues. Ingestion causes immediate

poisoning/damage to kidneys and liver May cause osteoporosis- loss of bone

mineral density Kidneys lose function to remove acids in

blood (proximal renal tubular dysfunction)

Cd Toxicity

Lead

General Human populations are exposed through air and food in equal proportions

Lead (Pb) is the most abundant toxic heavy metal

Mainly atmospheric depositions of industrial lead

Lead from shots- hunting

Sources

Side note: Drinking waterFound in piping: lead pipes, welding for copper pipes

City of Milwaukee adds phosphate to drinking water to prevent lead in pipes from dissolving into drinking water (adding to lake nutrient load)

Accumulation of Pb in sediment Accumulation of Pb organisms: All the way up the food web from plankton to

fishHigher accumulation in crayfish, bottom

feedersBioaccumulation in humans too: especially

fish consumers

Lead: Fate

Impacts:Nervous system increased blood pressure

in adultspathogenic effect:

directly interrupts the activity of enzymes

competitively inhibits absorption of important trace minerals

deactivates antioxidant sulphydryl pools through free-radical induced damage

Lead: Toxicology

Takes two forms in environment Inorganic Hg (metallic)

Less worrying as an environmental toxin Organic MeHg

Methyl MercuryBioaccumulates in tissuesBiomagnifies up the food chain

Mercury

Fate and Transport of Hg

Central Nervous system Damage Sensory and motor skill Impairment

Reproductive Effects Readily transferred across placenta Concentrates in fetal brain Physical behavioral defects Fetal death

Immunotoxicity Dose-dependent correlation in T-cell proliferation an MeHg

Genotoxicity Chromosome Breakage DNA strand Breakage

MeHg impacts to organisms and human health