Part 2: Chemicals and the Environment

Ecotoxicology

the effects of chemical contaminants on ecosystems (plants, animals, and other life forms)

Ecotoxicology major considerations

What are the contaminants

How do they disperse in the environment (Water, air, soil, etc)

How do the contaminants degrade

How are living species affected

How is the contamination detected, monitored and remediated?

Environment health toxicology

the effects of chemicals (usually contaminants) found in the environment on human health

Populations

A group of interbreeding individuals of the same species within a community (ex. A population of large mouth bass (Micropterus salmoides) in a lake; all humans (Homo sapiens) on this planet).

Community

a naturally occurring assemblage of populations of plants and animals that live in the same environment, are mutually sustaining and interdependent, and the are constantly fixing, utilizing, and dispensing energy

Ecosystem

Consists of communities of living organisms together with their habitat ( the abiotic environment) and includes the interaction among these compounds. Major ecosystems include deserts, forests, grasslands, tundra, and several types of aquatic environments

Contain biotic (living) and abiotic (non-living) components)

Terrestrial Ecosystems

Forests, Grasslands, Deserts, Tundra

Forests

The largest ecosystem, covering about 31% of land. They include Tropical Rainforests (the most biodiverse), Temperate Deciduous Forests, and Boreal Forests (Taiga).

Grasslands

Dominated by grasses rather than large trees, including Savannas(tropical) and Prairies (temperate)

Deserts

Arid regions with extremely low rainfall, ranging from hot subtropical deserts like the Sahara to cold deserts,

Tundra

Cold, treeless regions found in the Arctic or at high altitudes, characterized by low-stature vegetation like mosses and lichens.

Biome

A regional community of species that are adapted to live in similar conditions

Bigger than an ecosystem

Chemicals in different biomes

behave differently

Types of aquatic ecosystems

Freshwater, marine, estuarine

Freshwater Ecosystems Types

Lentic, Lotic, Wetlands

Lentic

Still or slow-moving (lakes, ponds, pools)

Lotic

Fast-moving (rivers, streams, creeks)

Wetlands

Saturated or inundated soil (marshes, swamps, bogs).

Marine ecosystems

High salt content (oceans, seas, coral reefs, estuaries)

Estuarine

Where fresh and saltwater mix (bays, river mouths)

Key components of aquatic ecosystems

Biotic (Living): Producers (algae, aquatic plants), consumers (fish, amphibians, insects), decomposers (bacteria, fungi).

Abiotic (Non-living): Water, temperature, sunlight, nutrients, dissolved gases, salinity

Chemicals move in our environment in 4 phases

air, water, soil, bioosphere

Air

contaminants enter via evaporation, stack emissions and tron the other phases. Transport within air is rapid.

water

contaminants enter via direct application, spills, wet and dry deposition.



Soil

contaminants enter via direct application, spills, wet and dry deposition and from other phases. Microbial degradation can be significant.



Biosphere

Chemicals move within Food webs, in some cases the chemical is very stable => increased concentrations, in other cases the chemical is unstable => decreased concentrations.

Movement and storage of chemicals in the environment

movement of chemicals from air, soil, and water into the biosphere (living organisms) depends on the chemical’s bioavailability

Bioconcentration

Directly non-dietary uptake of chemicals from the external environment

• Uptake (in fish) through their gills

Bioaccumulation

uptake of chemicals from the external environment via food

Biomagnification

increasing chemical concentrations at higher trophic (feeding) levels

Sublethal effects on individual organisms

Thankfully, most (but not all) chemical contaminants currently exist in relatively low levels or unavailable forms.

Chronic (sublethal) effects in populations

Reproductive success, Inhibition of growth rate, Predator avoidance behavior, Foraging behavior, Migration and homing, Alter breeding behavior, Nest-building and courtship,Territorial defense

These effects may occur even though

there is no measurable chemical present (e.q., rapid metabolism)

Mixtures of chemicals (common in the environment) may result in

effects not predictable from the effects of the individual chemicals.

Population and community effects

Abundance, age structure of the population, etc. Any effects on a population may ultimately have effects on the community since communities are collections of populations.

Community diversity, community composition

Bioconcentration - trophic levels and bioaccumulation

Build up of toxins in an animal due to passive exposure to toxins through gills or skin

Example: Fish take up toxins through gills due to living in contaminated water

Bioaccumulation - trophic levels and bioaccumulation

Build up of toxins in a single organism over time

Example: Deer accumulate toxins over time by eating contaminated plants

Biomagnification - trophic levels and bioaccumulation

Biomagnification = increase in toxin concentration in species at higher trophic levels

Example: Insects take up toxins from sediment, fish take up toxins from contaminated insects, eagles take up toxins from contaminated fish. Toxin levels increase up the food chain

DDT (insecticides) example

Bioconcentration, Bioaccumulation and Biomagnification of DDT, DDD & DDE (metabolites - affects breakdown) —> calcium in eggs —> thinner shells —> smaller population. Similar processes occur for mercury in fish and other persistent chemicals (PCBs and many others) in our environment.

Chemodynamics

the study of chemical release, distribution, degradation and fate in the environment

PCB uses

Electrical, heat transfer and hydraulic equipment

Plasticizers in pains, plastics and rubber products

Pigments, dyes and carbonless copy paper

Other industrial applications

PCB effects

manufactured from the 1920s and banned in 1979 by the EPS

cause cancer, immune effects (ex: killer whales), reproductive effects (ex: killer whales), endocrine effects

persist in the environment for decades

Housatonic River (PCB contamination, GE facility in Pittsfield, MA) - PCBs will degrade only over hundreds of years

From the CT Department of Environmental Protection (DEEP) - tells how to avoid PCB’s in fish, high risk vs low risk , what fish accumulates more PCB’s, what fish is safe to eat

Chemicals in the Environment and Human Health

Humans have most of the same cellular and subcellular processes as do plants and animals. We live in the same environment and are exposed to many of the same contaminants.

Environmental health therefore predicts effects on human health.

Concerns for Human Exposure risk

increased risk of various cancers, neurological problems and endocrine effects (EDCs) caused by the direct effects of relatively low levels of environmental contaminants that were used in the past or are still being used

Considerable toxicological research is directed toward

understanding the sublethal chronic direct health effects of these compounds on humans and ecosystems.

Why is causal linking of contaminant exposures to adverse effects in human population difficult?

Particularly when effects are not identified for many years and the causative agents) is/are no longer present. Since humans have a much longer life span than most other animals, low dose, chronic exposures may be significant.

Monitoring Water Quality

Testing water for chemicals of concern: streams, rivers, drinking water, well water, industrial water effluent, wast treatment effluent

Other monitoring

soil samples, air samples

using sentinel organisms for risk monitoring

Species can be collected and analyzed for toxic compounds

Useful species

Plentiful, easy to sample, prone to bioaccumulation of chemicals

Testing for exposure - catch and release strategies

Biomarkers and biomarkers of exposure

Biomarkers

Attempting to relate the presence of a hazardous chemical to a prediction of risk in an individual animal/plant, population, community or ecosystem.

Biomarkers of exposure

the presence of a chemical or its metabolite in an organism can be classified as a biomarker of exposure. In general, biomarkers of exposure are used to predict the dose received by an individual.

Convenient biomarkers of exposure and what they’re used for

exhaled air, urine, feces, blood, milk, hair, feathers —> drgu testing, breath testing, mercury in bird feathers

Biomarkers of animal heatlh

Biomarkers of effect

Biomarkers of effect

Measurable biochemical, physiological, behavioral, or other alterations within an organism that can be recognized as causing some type of toxicity

Biomarkers of effect examples

eggshell thinning by DDT/DDE, suppression of the immune system, hypersensitivity, high glucose levels, inability to capture prey, low birth rates, high infant mortality, altered migration, courtship behavior, etc.

Trophic levels in ecosystems

Decay detrivores (get energy from food) —> producers —> herbivores, primary predators, secondary predators

Autotrophs

Plants - make their own energy

Heterotrophs

Herbivores, primary predators, secondary predators - get energy from food

How have humans changed metals?

Have changed distribution and biochemical form

Interest no longer focused on preventing acute toxicity, but

chronic long-term effects of metal exposure

Convenient biomarkers of exposure to metals

blood, urine, hair

Metals of special toxic concern

Cr, Cd, Hg, Pb, As

Where do metals come from?

Essential metals

Essential calcium (Ca), phosphorus (P), potassium (K), sodium (Na), iron (Fe), iodine (I), copper (Cu), manganese (Mn), zinc (Zn), cobalt (Co), molybdenium (Mo), selenium (Se), nickel (Ni), vanadium (V), silicon (Si) - metalloid

Why are essential metals needed for normal functioning? - Ex: Iron

Protein hemoglobin - carries oxygen in blood, heme groups (4) - contain iron atom - can bind to/carries oxygen or carbon dioxide

Toxic essential metals

Cobalt

Non essential

everything else - lead, mercury, arsenic - metalloid, chromium, cadmium

Toxic non essential metals

Lead, Mercury, Arsenic, Chromium, Cadmum

Essential metals are ____, whereas non-essential metals are _____, but __

Needed for life, common, toxic

Shape of dose response curve - essential metal deficiency and toxicity

Cobalt (Co)

Important in vitamin B12

Copper (Cu)

Important for many enzymes

Iron (Fe)

Iron deficiency is very common in the US, affecting older infants, young children and women of childbearing age, causes anemia, impaired brain development, decreased resistance to infections

Accidental ingestion of iron-containing medicines in children

Ingestion of > 2.5 g of Iron sulfate can result in acute toxicity - acute iron poisoning

Magnesium (Mg)

Important for many enzymes. Toxicity when magnesium containing drugs (usually antacids), are ingested over long periods of time.

Zinc (Zn)

More than 200 enzymes require Zn and Zn is essential for development and normal function of the nervous system.

Most Zn is from food.

Deficiency results in delayed growth and sexual maturation, dermatitis, and degenerative disorders of the nervous system

Anthropogenic and Natural metals in the environment

Metals vs compounds

Humans cannot create or destroy metals (and other elements) except through nuclear chemistry.

However, humans can influence the amount of chemicals in the environment (by release through industrial processes)

In contrast, humans can readily create compounds through chemistry.

Compounds are composed of elements, and chemistry can rearrange the order of elements within compounds

Interactions with other essential metals

Occurs when the body uses a non-essential metal (Hg, Cd, Pb) in place of an essential metal. For example, Lead (Pb) is similar to calcium and interferes with the calcium-dependent release of neurotransmitters (so it is a neurotoxin) and can also bioaccumulate in bone.

Age and stage of development

Major exposure to children is via food, high milk diet (high lipid content) increases metal absorption; also accidental ingestion by children (e.g., lead paint chips).

Lifestyle factors and diet

Cigarettes contain cadmium (Cd) and smoking alters pulmonary effects of metals.

Alcohol alters diet and reduces essential metal intake.

Occupational exposure (miners etc.)

Immune status

Metals that can cause immune reactions include Au, Pt, Be, Cr, Ni 5.

For many metals (Cd, Cr, Hg, Li) mechanisms of toxicity are

not entirely known

Lead toxicity

Nervous system-cognitive (IQ), hearing acuity and behavioral defects seen in chronically exposed children

Acts by impairing neuronal cell-cell connections, interferes with neurotransmitter function, competes for uptake of Ca by mitochondria.

Current FDA permissible levels in baby foods are:

• 10 ppb for fruits, vegetables, mixtures, meats

• 20 ppb for root vegetables

• 20 ppb for dry cereals

Lead is a possible

carcinogen

Lead in commercial products

Sure Grip Paint Brushes Recalled by Early Childhood Resources Due to Violation of Lead

Paint Standard

United Scientific Recalls Magnets Due to Violation of Lead Paint Standard

Mercury toxicity

Hg distributes globally as a vapor in the atmosphere.

Eventually returns in rainwater, then methylated by microbes to produce methylmercury, then enters aquatic food chains and can become bioaccumulated and biomagnified, reaching our food supply (mostly protein and fish).

Also, occupational exposure (extraction of gold) and in dental amalgams (fillings).

Concerns about amalgam fillings

Neurobehavioral Effects of Dental Amalgam in Children: A Randomized Clinical Trial

Amalgams contain 50% liquid Hg (+ silver (~27%), tin (~15%) & copper (~8%))

Mercury persistence

Industrial Mercury Poisoning

Vinyl Chloride and acetaldehyde plants used HgCh as catalyst.

700 cases of poisoning & >70 deaths

Minamata disease victim

Mercury and methylmercury

Mercury in ecosystems

methylmercury: bioaccumulation and biomagnification

Mercury accumulation and trophic levels

____ fish accumulate mercury

Older/larger

Arsenic (As)

5 to 20 ug/day in our food and water (and some inhalation (cigarettes)); excretion is relatively rapid (a few days) & mainly via urine. Probably an essential metal in trace levels.

Arsenic (at high concentrations) is a mitochondrial toxin that acts by blocking the production of ___ and increases ___.

ATP, ROS

70 to 180 mg Arsenic as a single dose

may be fatal

Symptoms:

Chronic exposure (>1 mg/day?) may lead to fever, anorexia, cardiac arrhythmia, neurotoxicity.

Known skin and lung carcinogen (dose???)