Most mercury enters aquatic environments from the atmosphere
The dominant inorganic forms are Hgo and Hg2+.
Positively charged Hg2+ can become attached to negativelycharged organic and inorganic particles in soils and sedimentswhich tends to immobilize them.
Under anaerobic conditions, Hg2+ can be converted to organic Methylmercury which is more toxic and persistent in organisms.
Mercury methylation is related to the metabolism of Sulfur-reducing bacterial under anaerobic conditions
The exact biochemical mechanism is poorly understood.
High sulfur concentrations increase mercury methylation
Mercury
The following are required for mercury methylation
Inorganic MercuryAnaerobic Conditions
Carbon Source (sediments)Sulfate/Sulfate-Reducing Bacteria
Methylmercury is more directly toxic and remains inThe tissues of organisms longer than inorganic Hg2+.
This allows methymercury to bioaccumulate in organisms
Bioaccumulation allows for biomagnification whichis the increase in concentration of a chemicalin organisms higher up in the food chain.
Bioaccumulation occurs when an organism absorbs a toxic substance at a rate greater than that at whichthe substance is lost from the body.
Biomagnification: concentration of a chemical in organisms as it moves up the food chain.
Organisms near the top of the food chain may have concentrationsof mercury millions of times greater than in the aquatic environment
Synthetic Organic Chemicals
DioxinsPesticidesPCBsFlame Retardants
PBDE
Dioxin
PCBDDT
Organochlorines
Organic = carbon-rich compounds
Viktor Yushchenko Ukrainian President
Potential Toxicity
6,000 times the usual concentration in his body
July November
the second highest dioxin level ever measured in a human
2004
Chemicals like dioxin are acutely toxicIn high doses, but they also can bioaccumulate
creating chronic toxicity at lower doses
The cause of their ability to bioaccumulate is related to their water solubility.
Organic Chemicals
Greases, Oils, Paints, Pesticides, Industrial Chemicals
Grease and Oil
Carbon 83 to 87%
Hydrogen 10 to 14%
C16H14OS
Oil Paint
Composed mostly of carbon and hydrogen,and possessing no electrical charge.
Carbon-rich compounds
Dioxin
PCB
DDT
Principally carbon, hydrogen
C11H18O2Cl4
C14H22Cl5
C12H21Cl2
Do not possess an electrical charge
These types of chemicals are poorly soluble in water
In what substances do they dissolve?
Greases, Oils, Paints, Pesticides, Industrial Chemicals
Organic Solvents
water
Hexane
Acetone
Lipids
Carbon-based compoundsdissolve more easily in carbon-based solvents.
carboncarbon
carbon
carbon
Dioxin
-SO4
SoapSoap
hydrophobichydrophilic
SO4-
SO4-
SO4-
SO4-
SO4-
SO4-
SO4-
SO4-
High Carbon Concentration
Fundamental similarity betweenthe chemical and the solvent.
Bioaccumulation in Organisms
Lipid Tissue in Organisms
The chemical essentially dissolves into the lipid tissues
carbon
Synthetic organic chemicals are poorly soluble in water
They are soluble in organic solvents and lipids
Lipids are found in all organisms
Despite low levels of organic chemicals in water dueto their low water solubility, high amounts canaccumulate in the tissues of living organisms
Bio-Magnification
Water and phytoplankton to zooplankton: 800 x
Zooplankton to fish: 31 x
Overall: 120,000 times original concentration in water
Fish to eagle: 4.8x
PCBs
Electrical equipmentplasticizers in paints, plastics and rubber productspigments, dyes and carbonless copy paper
PCBs were “banned” in 1979
Used as insulating fluids and coolants in electrical equipment and machinery from 1929-1977.
EPA estimates that 150 million pounds of PCBs are dispersed throughout the environment,including air and water supplies; an additional 290 million pounds are located in landfills in this country
some PCBs act like hormones, and other PCBs are nerve poisons
PCBs in Marine Mammals
HazardousWaste level(Canada)
Killer Whales(1000 ppm)
High on food chainLipid tissues
Seawater
Arctic cod muscle
Narwhal blubber
14 - 46 ppb
0.0003 ppb
2440 - 9160 ppb
Toxaphene
50,000 X
~ 8 M X
carbon lipid400,000 tons: 1946 to 1974
(670 chemicals)
1. Many synthetic organic chemicals are uncharged.
2. Because they are uncharged, they do not permit orientation of water molecules and are poorly soluble in water.
3. Ionic compounds (e.g. NaCl) are about 1 billion times more water-soluble than uncharged organics.
4. Uncharged organic chemicals, however, tend to be soluble in organic solvents and organic materials because of similar carbon-based chemistry.
5. These materials can include lipid tissues in organisms which can lead to biomagnification
Summary
Solubility
water
Hexane
Acetone
Lipids
Carbon-based compoundsdissolve more easily in carbon-based solvents.
carboncarbon
carbon
carbon
Dioxin
Where in these environmentsdo we find high levels of carbon?
Many synthetic organic chemicals, particularlythose like PCBs and DDT are very persistentin the environment. They last for decades.
They become stored in organic materialsthat naturally occur in aquatic and terrestrial systems
CarbonHydrogenOxygen
Organic MatterOrganic Matter
Coiled and convoluted chains of carbon, hydrogen, and oxygen
CarbonHydrogenOxygen
Organic MatterOrganic Matter
COOH
OH
carboxylic
enolic
CCCCCC
CC
CC
C
C
C
C
C
H
H
H
H
H
H
HH
HH
H
H
H
Partitioning of neutral organic chemicals into soil organic matter limits their mobility in the environment
Water
Organic Sediments
Environmental Persistence
Solubility of < 0.1 μg/L
Organic chemicals become stored in organic sediments
This protects them from degradation and increases their lifetime in the environment
DDT
Lake Michigan
µg PCB/Kg sediment (parts per billion)
EPA 2004
mg Carbon /g sediment
N Concentration
Organic Carbon
PCBs
PCBs
“banned” in 1979
Open water PCB concentration = < 1 part per trillion
DDT
dichloro-diphenyl-trichloroethane
First Modern Pesticide
Insecticide developed to combat insect-borne disease
Use was later expanded to include agriculture
DDT levels ranging from 2,200 to 110,000 µg/kg (ppb) in organic soils and sediments.
Rita Island, Okeechobee
Organic soils
Historically characterized by clear water and a highly prized sports fishery, it served as a popular destination for boaters, swimmers, and fishermen for decades.
Lake Apopka
30,800 acres
mean depth is 5.4 feet
15 miles northwest of Orlando
In the 1970s, scientists considered Lake Apopka a prime place to harvest eggs and hatchlings to studythem in captivity.
In 1980 and 1981, scientists counted populations of 1,200 to 2,000 alligators in a single night on the lake
By the late 1980s, they counted only 150 per night
AgricultureAgriculture
Pesticide Use in Agricultural Area
Pesticide use included high amounts of DDT
"Lake Apopka is a big chemical soup," Michael Fry, a researcher from the University of California
Tower Chemical Company
Produced dicofol, a mixture of the pesticide DDT and DDE, a by-product of DDT. Periodic spills occurred there, but a particularly large accident in 1980 caused dicofol to spread into the lake
TOC content ranges from 33 to 37%
Apopka's juvenile alligators have abnormal testes and ovaries and abnormal hormone balances
DDE, a breakdown product of DDT, is a major contaminant in Lake Apopka
DDE is known to block the action of testosterone
Alligator Population crash was linked to poor egg viability
Estradiol Testosterone
Apopka males had high levels of estradiol relative to testosterone
' Teeny Weenies '
Alligators in Florida's Lake Apopka have Smaller Penises
Kyla Dunne for PBS June, 1998
http://www.mindfully.org/Pesticide/Alligators-Apopka-PBS2jun98.htm
Solubility
water
Hexane
Acetone
Lipids
Carbon-based compoundsdissolve more easily in carbon-based solvents.
carboncarbon
carbon
carbon
Dioxin
-SO4
SoapSoap
hydrophobichydrophilic
SO4-
SO4-
SO4-
SO4-
SO4-
SO4-
SO4-
SO4-
High Carbon Concentration
An Important Organic Solvent:Octanol
C8H18O
Neutral organic chemicals are soluble in organic solvents
cc c
c cc c
c
Octanol-Water Partitioning
Octanol and water are immiscible
Octanol Density: 0.824 g/cm3
octanol
water
C8H18O
C8H18O
Octanol-Water Partitioning Coefficient
Kow = Concentration of chemical in octanolConcentration of chemical in water
At equilibrium
water
1 L Octanol1L Water
Add 10 mg chemical
separate
chemical
chemical
Analyze the water phase for the chemical.Difference between initial amount and amount in water = amount in octanolThe ratio between the two yields the Kow
octanol
Add 10 mg chemical
separate
chemical
chemical
0.01 mg L
9.99 mg L
Water phase octanol phase
Kow = 9.99 mg L
0.01 mg L
= 999
1 L Octanol1L Waterl
Kow of some Organochlorine Compounds
DDT 4,000,000
PCBs 2,000,000
Dioxin 6,000,000
A high Kow indicates strong interaction with organic solvents and lipid tissues
chemical in octanolchemical in water
PCBs
Electrical equipmentplasticizers in paints, plastics and rubber productspigments, dyes and carbonless copy paper
Kow = 2,000,000
PCBs were “banned” in 1979
Used as insulating fluids and coolants in electrical equipment and machinery from 1929-1977.
EPA estimates that 150 million pounds of PCBs are dispersed throughout the environment,including air and water supplies; an additional 290 million pounds are located in landfills in this country
some PCBs act like hormones, and other PCBs are nerve poisons
DDT
first modern pesticide (Nobel Prize, 1948)
Insoluble in water. Soluble in
most organic solvents, fat, and oils.
used with to combat mosquitoes spreading malaria (mosquitoes),
and typhus (lice)
Banned in 1972 (U.S.)
Kow = 4,000,000
Launch of the Environmental Movement
1962human volunteers ingested 35 mg of DDT
primates were fed 33,000 times more DDT than the estimated exposure
Thinning egg shells
Lower hatching rates
Declining Eagle population
Carcinogenic
decline in the eagle population occurred before the DDT years (bounties between 1917 and 1942)
http://faculty.unionky.edu/rbotkin/RECM_480_ISSUE_16A_YES_BLUE.PPT#291,22,Issue%2016:%20Yes
Activated CarbonActivated Carbon
Activation by heating
Extremely porous with high surface area: 500 m2/g
Large surface area = high contact with contaminants
Activated CarbonActivated Carbon
Absorption: spontaneous movement of primarily organic contaminants from water to carbon matrix.
Pesticides and other organics essentially dissolve in the carbon
Chlorine sticks to the extensive surfaces
2,4-D2.4.5-TP (Silvex)AlachlorAtrazineCarbofuranChlordaneEndrinHeptachlor EpoxideLindaneMethoxychlorSimazineToxapheneBenzeneCarbon TetrachlorideChlorobenzene
EthylbenzeneMonochlorobenzeneMTBEO-DichlorobenzeneP-DichlorobenzeneStyreneTetrachloroetheneTolueneTrichloroetheneVOCsAntidepressantsSteroids/HormonesPrednisone, Prednisolone,Progesterone, Testosterone,Cortisol/HydrocortisoneAntibioticsCiprooxacin, Trimethroprin,SulfamethoxazoleAnxiolyticsMeprobamate
Carbon Filter Removal
Does not remove bacteria or most metals