Environmental Hazards - All Parts

Pesticides

(WHO) definition: chemical compounds used to kill pests, including insects, rodents, fungi, and unwanted plants

(US EPA): any substance or mixture of substances intended for preventing, destroying, repelling or mitigating any pest

• chemical pesticides are used for agricultural purposes

General Characteristics of Pesticides

• Lipophilic - soluble in fat

• sometimes slow to degrade in the environment and in the body (bioaccumulation)

• Commercial pesticides: mixtures containing the active ingredient and by-products, propellants, surfactants, etc

Combined properties of the components can affect toxicity and other characteristics of a pesticide (e.g synergism: 1 + 1 = 5)

Types of Pesticides

Systemic: absorbed and distributed throughout the plant, providing protection from pests that feed on various parts of the plant

• works from roots up

Contact: applied directly to the surface of plants, soil, other substrates to control pests on contact

Broad-spectrum: targets and controls a wide range of pests

• downside?: non-target animals & plants are also affected

Narrow-spectrum: specific to particular types of pests

Organophosphates

Developed during WWII for use as chemical (nerve gas) weapons

• mode of action: irreversibly inactivating acetylcholiine-esterase which regulates acetylcholine, leading to an increased accumulation of acetylcholine. This disturbs transmission of impulses at the nerve & muscle endings

• small amounts can be detected in food and drinking water

Carbamates

• used for insecticides

• mode of action: reversibly inactivates acetylcholine-esterase

  • e.g carbaryl

Organochlorines

• insecticides

• Mode of action: opening sodium channels in axonal membranes leading to spontaneous depolarization

• persistent in the environment and many have been banned by the US EPA and the WHO

Pyrethroids

• synthetic form of pyrethrins

• typically insecticides used for agricultural and household purposes

• majority of household insecticides are composed of pyrethroids

Neonicotinoids

• high degree of selectivity toward insects

  • chemically similar to nictotine

Herbicides

• most COMMONLY used pesticides

• weed killers - stunt or kill unwanted plants

• product usually contains side products (emulsifiers, dispersants) in addition to the herbicide —> increases toxicity to humans

• General toxicity: dermal irritation, allergy, asthma

• chronic low dose exposure related to hormonal/reproductive/genotoxic/carcinogenic effects

Glyphosate

most WIDELY used herbicide in the world today

• used on millions of acres of crop land, and in urban/home application

• works (in plants) by inhibiting synthesis of some amino acids

Dissipation Pathways

The way pesticides can be transported by wind, water, and through soil

Pathways:

• spray drift (by the wind)

• surface run-off and wash-off (by water)

• volatilization (influenced by temperature)

• Scorption/retention and microbial/chemical transformations (in the soil)

• leaching (through the soil)

• foliar interception and plant uptake (by plants)

Effects on the Environment

Soil:

• biodiversity loss in the soil —> less nitrifying micro-organisms leading to less fertile soil

• less organic matter: less retention of water, more build up of pesticides

creates vicious, degradation cycle of less fertile soils needing increased use of fertilizer

Environmental Effects on Wildlife

• disturbs symbiotic relationship between nitrogen fixing bacteria and plants

  • affects plant growth and indirectly animals

• direct effect on animals through dietary exposure (ingesting contaminated food and water)

Adverse Health Effects

Acute: poisoning leading to dizziness, headaches, convulsions, loss of consciousness

Chronic: occupational (farmers), dietary exposure leading to neurological/neurodegenerative diseases (Alzheimer, Parkinson)

• Children are vulnerable to pesticides b/c of curious behavior and less physiological size —> slower metabolism of toxicants

• some pesticide classes have properties mimicking hormones and affecting multiple organ systems and functions (reproductive health and cancer risk)

• Exposure to toxicological insecticides can affect the central nervous system

General Properties of Metals

• Metallic: metal atoms bonded to each other

  • e.g copper wire

• Ionized: the metal atoms are charged, and bonded to a non-mental element

  • e.g NaCl

• Organic: bound to carbon-containing molecules

  • e.g methyl-group added to a metal

The “Good” of Metals

• Intra and intercellular communications

• maintaining electrical charges (proper functioning of nerve cells, muscle cells, brain & the heart)

• maintains DNA integrity by participating in various biochemical processes involved in DNA repair/stabilization/protection against oxidative damage/regulation of DNA-binding proteins

Lead Exposure

naturally occurring, exposure mostly due to human activities

Lead - sources of exposure

• drinking water: lead water service lines, lead connections, lead-based plumbing materials

• Food: contaminated water bodies, wild birds & game containing lead shot

• cosmetics

• lead-based paint (seen in older homes & buildings)

Lead - Biologic Fate

Distribution to:

• bones and teeth (half life: 25 years)

  • where most of lead is found in adults

• distributed to other parts of the body, but very slow; faster in times of physiological stress (pregnancy, fasting, starvation)

• total lead in the body determines the burden

Lead - Exposure Routes

• Ingestion: absorption from G-I tract to distribution to other organs and excretion

  • increased absorption during pregnancy, fasting, childhood & mineral nutritional status

• Inhalation: can be absorbed up to 100%

• humans mostly exposed to INORGANIC PB which DOES NOT metabolize in the body

• ORGANIC lead compounds METABOLIZE in the liver

  • generally considered less toxic due to higher bioavailability

Lead - adverse health effects

• low levels primarily affect the nervous system

  • unborn child, neonates, infants, and children most sensitive to neruotoxic effects

    • have a more permeable blood-brain barrier

• Pregnant women: lead is released from the mother’s bones along with calcium, has detrimental effects on developing fetus & infant

• Adults: relatively LOW lead concentrations affect central nervous system (CNS); causes:

  • fatigue

  • poor concentration

  • behavioral changes

• Peripheral nervous system (PNS) effects:

  • affects nerves transmitting signals to muscles

  • “wrist drop” —> extensive exposure to lead paint

• cardiovascular effects, increased blood pressure & hypertension, decreased kidney function, reproductive problems (in men + women)

Mercury

• naturally-occuring, found in earth’s crust and in deposits of of coal

• found in 3 forms: elemental (metallic), inorganic (mercury salts), organic (methylmercury)

  • methylmercury bioaccumulates in organims

• the form of Hg determines the distribution and effects in the body

Mercury Sources

• natural: volcanic activity

• anthropogenic: burning of fossil fuels; coal fired power plants

Mercury Uses

• used in veterinary and human medicine as topical antiseptics

• Thimerosal: used as antibacterial preservative to prevent growth of dangerous bacteria and fungus

  • is an ORGANIC form used in vaccines w/ more than one dose

  • low concentration doesn’t have any adverse health effects

Mercury: acute vs chronic exposure

Acute: primarily occurs with vapors from elemental Hg

• rare acute exposure with ingestion of inorganic or methyl mercury

Chronic toxicity: more common

• consumption of fish containing Hg

Disruption and effects on health of Mercury

• Ionic form: MOST toxic, but don’t cross membranes well

• Hg vapor: absorbed by inhalation & readily diffuses across lipid membranes of cells

• Methyl Hg: 95% absorbed by oral route

Concerns of Methyl Hg

• common environmental contaminant

  • Minamata Bay, Japan —> abundance of fish high in methyl-Hg

  • effects on health: reproductive, developmental, renal, and neurotoxic effects and death

  • Iraq: Hg-treated grain (against pests) that was intended to be planted, was consumed

Arsenic

• naturally occurring element widely distributed in the earth’s crust

• CANNOT be destroyed in the environment, only changes form

  • inorganic and organic

  • INORGANIC FORM IS HIGHLY TOXIC

    • exposure routes: ingestion - water & rice, dermal - contaminated soil, dust

• Organic form - less to non-toxic

  • exposure through seafood consumption

Sources of Arsenic Exposure

Anthropogenic:

• mining

• burning of fossil fuels

• pesticide fertilizers

• industrial waste

Natural:

• volcanic eruptions

• forest fires

• soil

• rock weathering

• groundwater

Arsenic & Adverse Health Effects

• breathing high levels of inorganic arsenic cause sore throat/irritated lungs

• Chronic toxicity: neurotoxicity, hepatotoxicity, cancers

Benzene

• Volatile Organic Compound

• primarily ANTHROPOGENIC

  • widely used in the U.S for production volume

Benzene Exposure

• breathing in airborne benzene

• skin contact with gasoline and other liquids containing benzene

• drinking benzene-contaminated water

Benzene ADME and Toxicology

• Absorption: inhalation, ingestion, dermal

• Body Distribution: bone marrow and high lipid content tissues

• causes CNS and Hematologic effects

Benzene Exposures

• Outdoor air levels are less than indoor air levels in terms of benzene levels

  • outdoor emits from tobacco smoke, gas stations, motor vehicle exhaust, industrial emissions

  • indoor emits are from glues, paints, furniture wax, detergents

• also leaks from underground storage tanks that can contaminate well water

• Those most at risk:

  • steel workers

  • gas station employees

  • workers in petrochemical/coal/rubber tire companies

  • tobacco smoke

Benzene Neurological Effects

• Acute: solvent effect

  • CNS neurodepression

• Chronic - repeated long-term exposures

  • e.g Painters syndrome (sniffing)

• Chronic toxicity in the hematopoietic system

  • damage of pluripotent stem cells of the bone marrow

Cadmium

• soft, malleable, bluish white metal

• found in tiny amounts in air, water, soil, food

• used in paints, batteries, electronics, by-product of smelting, tobacco

• contaminant of grains (e.g rice), and in seafood from contaminated water bodies

Cadmium Toxicity

• low uptake from gut & very slow excretion rate

• classical nephrotoxic agent (kidney disease)

• recognized as a carcinogen

Chromium

• naturally occurring

• used in metal plating, paints, electronics, steel making

• +3 and +6 valences are common

  • +6 forms are genotoxic (toxic to genetic material)