Slide Types of toxicants

Phosphorus P 4 - yellow form very reactive and therefore highly toxic - red form found in matches - essential nutrient mostly in the form of phosphate: PO 4 3- ; key element in DNA, R

TOXIC NON-METALS & METALLOIDS

Halogens (F 2 , Cl 2 , Br 2 , I 2 )

- very reactive and therefore highly toxic

- reaction products usually toxic

- when covalently bond, typically increases toxicity and persistence of organic

compounds

- in ionic form, Cl, I (and F) are essential nutrients; Br - , I - and F - are toxic at

relatively low levels

- Common uses: disinfectant (in water Cl 2 forms hypochlorous acid, a.k.a bleach; betadine = I - plus I 2 in water); in cleaner (HCl); chemical synthesis

(everything organic with halogen bound to it: pesticides, PVC)

- inorganic Cl and Br compounds are made by some sea weeds for

disinfection purposes

Phosphorus (P 4 )

- yellow form very reactive and therefore highly toxic

- red form found in matches

- essential nutrient (mostly in the form of phosphate: PO 4 3- ); key element in DNA, RNA, ATP

- Phosphine (PH 3 ) is common insecticide and rodenticide

- covalently bond to organic compounds: pesticides, fire retardants

Sulfur (S x )

- in various forms used as fungicide, since antiquity

- S containing compounds have typical smell

- essential nutrient (S containing amino acids)

- common uses: gun powder, sulphuric acid, preservative (sulfite in wine

suppresses yeasts)

Arsenic (As)

- in various forms used as pesticide, since antiquity

- famous poison: killed Napoleon

- used as wood preservative, pesticide and in metal alloys

- sometimes present in natural environments at relatively high levels

- some ores have high As content; smelting releases this As

Selenium (Se)

- essential micronutrient but toxic at low levels (mind your supplements!)

- mimics S in biochemical reactions, hence its toxicity

- used in semi-conductors, pigments

Fertilizers (PO 4 3- , NO 3 - , NH 4 + , urea)

- At low levels, not directly toxic (except ammonia to some extent)

- alter species composition, especially in sensitive habitats

- may cause algal bloom and deprive environment of oxygen

- may cause toxic organism to grow explosively (red tide, cyanobacteria)

TOXIC METALS

Tin (Sn)

- in inorganic form relatively little toxic

- in organic form used as fungicide (cyhexatin) and antifouling agent TBT

(tributyltin) TBT is extremely toxic, especially for molluscs

- common uses: coating of iron to prevent oxidation, pots and flatware (all

these uses mostly obsolete)

Mercury (Hg)

- fluid at room temperature (quick silver)

- easily forms covalent bonds with organic compounds, which are extremely

toxic (cf Minamata disease)

- complex behavior in environment (speciation, cycling)

- common uses: thermometers; amalgams (dentistry, gold mining), batteries,

paints, fungicides

Lead (Pb)

- most widely distributed toxic element, mostly because of its use in the past

(lead based paint, tetraethyl lead in gasoline, lead arsenate as insecticide, solder, piping – now all obsolete in the West)

- still used in batteries, lead crystal, ceramics, ammunition and as weights

(fisheries, wheel balancing) and released during smelting of ores

- Pb 2+ causes anemia and neurological dysfunction

Cadmium (Cd)

- closely associated with zinc (a micronutrient), which it (as Cd 2+ ) mimics

biochemically, hence its toxicity (also a carcinogenic)

- forms complexes with ligands, especially S containing

- common uses and sources: by product of zinc mining, nickel-cadmium

batteries, plastic stabilizers, pigment, vulcanized rubber

Chromium (Cr)

- essential micronutrient, occuring predominantly as Cr(III) and Cr(VI)

- hexavalent form is especially toxic (carcinogenic, kidney necrosis)

- toxicant in ‘Erin Brokovitz’ movie

- used in chrome plating, tanning, pigments, wood preservation

Nickel (Ni)

- common element in earth crust

- Nickel compounds (Ni 2+ ) are very toxic and carcinogenic; in elemental form,

it causes contact dermatitis in sensitized individuals

- used in alloys to prevent corrosion (stainless steel, coins), ni-cd batteries

Aluminum (Al)

- after iron, most common metal in earth crust

- free Al 3+ is toxic, but sufficiently high concentrations only occur at low pH (acid main drainage, acid rain mobilizing free Al 3+ in soils)

- widely used in elemental form in construction, sheet metal

- radiation does not lead to contamination

- a short half life implies a lot of radiation (and potential damage) in a short

time; waste management is easy

- a long half life implies relatively little radiation over an extended period of

time; waste management is problematic

- many isotopes accumulate to high levels in some tissues and organs, causing

locally much damage

Examples

- 14 C, naturally occurring, long half life, used in dating

- 3 H (tritium), low energy, medium half life, used in tracer studies

- 131 I, short half life, accumulates in thyroid gland, medical uses

- Radioactive isotopes of essential elements, mostly short half life, used in

biochemical studies

- 60 Co, medium half life, radiotherapy of cancer

- Cs, Sr, I isotopes of major concern produced during nuclear explosion

- U and Pu isotopes, fuel of nuclear reactors and bombs U extremely toxic in

its own right

OH groups increase solubility

Carboxyl groups increase solubility more and are acidic

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HYDROCARBONS

- some have extensive industrial application

- in the past, uncontrolled dumping of those has led to wide spread contamination

Cl Cl

wide spread contamination liver and kidney damage

Monomers of PVC Cl

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3 ALIPHATIC ORGANOCHLORINE

INSECTICIDES

- low water solubility

- highly lipophilic (high bioaccumulation potential)

- very persistent (once seen as an advantage)

- highly toxic for mammals

- old fashioned insecticides still found in the environment

Cl

Cl Cl

Cl

Cl

Cl

1,2,3,4,5,6-hexachloro-cyclohexane Lindane

ClCl

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4 AROMATIC HYDROCARBONS

Pyrene Naphtalene

Benzene

Anthracene Fluorene

- low polarity, lipophilic, accumulate in sediments

- polycyclic aromatic hydrocarbons (PAH) have 2 or more

fused rings

- acute toxicity, carcinogenic

- major source: petroleum, incomplete combustion of

organic material

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5 AROMATIC INDUSTRIAL BASE

CHEMICALS

- production of plastics and other polymers

- formed during burning of biomass

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NOT ALL AROMATICS ARE (VERY) BAD

- aromatics are aromatic

- many natural tastes and scents are simple aromatics derived from phenol, i.e., rosemary, geranium, lavender and

Anisol

O H

CH O Vanillin

- many have antiseptic (i.e., toxic) qualities

- key aromatic in biodegradation

CH 2

C O

OH

Benzoic acid

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6 HALOGINATED AROMATICS

- mostly low water solubility

- highly lipophilic (high bioaccumulation potential)

- very persistent (used to be a big plus)

- many are very toxic

- many are banned (in US) or use is severely restricted but are still major environmental contaminants

Cl

Cl

Cl Cl

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8 DDT

- insecticide with ‘low’ toxicity for mammals

- once the magic bullet against malaria, now infamous

- banned in US since 1972

- insect develop resistance, hence higher application loads

- DDD and DDE major degradation products found in

environment

CH

C Cl Cl

Cl

CH

C Cl Cl

H

C C

Cl H

p,p' DDT (dichloro-diphenyl-trichloroethane)

p,p' DDE p,p' DDD

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9 POLYCHLORINATED PHENOLS

- major sources: bleaching of wood pulp, wood preservatives

- water soluble acids, reactive, form dioxins

OH

Cl

Cl

OH Cl

Cl

Cl

OH Cl

Cl

Cl Cl Cl

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10 DIOXINS (PCDD) AND DIBENZOFURANS (PCDF)

- formed as unwanted by-product of chemical synthesis,

notably during the synthesis of the herbicides 2,4,5-T and 2,4-D, and in solutions containing polychlorinated phenols

- produced during combustion of organochlorine

compounds, especially PCBs

- highly persistent in the environment, accumulate in

sediments and body fat

O H

Cl

dibenzo-p-dioxin

2,3,7,8-tetrachloro-O

Cl

Cl

Cl Cl

2,3,7,8-tetrachloro-dibenzofuran

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11 ORGANOPHOSPHORUS AND CARBAMATE INSECTICIDES

- neurotoxins (inhibitors of acetylcholinesterase)

- most toxic for invertebrates

- low environmental persistence; acute toxicity is main concern

CH 3

Carbaryl R

O

C

N O

CH 3 or H

CH 3 Carbamate insecticides Primicarb, Carbofuran

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12 PYRETHROID INSECTICIDES

- synthetic analogs of natural pyrethrins (Chrysanthemum)

- esters of chrysantemic acid and an organic base

- rapid biodegradation (short term toxicity)

- low water solubility, adsorption to particulate matter

- low mammalian toxicity but toxic for fish, invertebrates

C CH

C

H 3 C

H 3

C H

CH C

CH 3

CH 3

C O OH

Chrysanthemic acid

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13 AROMATIC HERBICIDES

a SYNTHETIC ANALOGS OF INDOLE ACETIC ACID

- plant hormones stimulating growth: 2,4-D; 2,4,5-T, MCPA, CMPP

- uncontrolled growth leads to death of plants

- more toxic to dicotyl than monocotyl plants; hence used in cereal crops and grass

- mostly readily biodegradable

- as defoliant used in Vietnam (Agent Orange)

- can be contaminated with dioxins (ring is chlorophenol)

CH C C

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B PIRIDINE HERBICIDES

- contain piridine ring (also in DNA, RNA)

- water soluble (contamination of aquifiers)

- charged, readily bind to negative soil particles

- uncontrolled growth leads to death of plants

- heterocyclic compounds with 3 N’s in ring

- high water solubility, biodegradable

- higher toxicity for dicotyls

NN

H 3

CH

CH 3 C

H 3

Atrazine

garlic odor in old hotel rooms