ENVSCI 201: Lecture 8 - Traditional Sources of Contaminants

Variety of Contaminants

Contaminants vary in several ways:

• Structure: systematic, nomenclature, etc

• Compartment: systems they can move and distribute in

• Effects: carcinogen, endocrine disruptors, etc

• Phsyio-chemical Properties: hydrophobic, polar, ionic, persistent, etc

• Sources: point source, diffuse source

Point Source Contaminants

A well defined direct source in time and space, you can actually point at where a contaminant is coming from

Some examples include a leaking pipe, an oil spill, and so on.

Diffuse Source Contaminants

Coming from multiple different dispersed sources.

Some examples include urban runoff, atmospheric deposition, and so on.

Underground Storage Tanks & Groundwater Contamination

Storing chemicals in an underground storage tank is a common practise across many industries. However, there are times when they can start degrading and leaking underground, possible into groundwater.

It is a good example of a point source. The petrol industry uses them to store BTEX while the cleaning industry uses them to store spent chlorinated solvents.

BTEX

Benzene, toluene, ethylbenzene, and xylenes, which are naturally occuring hydrocarbons that anthropogenic activities has amplified. They’re volatile compounds found in gasoline.

Long-term exposure to them has links to cancer and brain damage while inhalation may cause headaches, irritation, and reduced coordination.

Chlorinated Solvents

Chemivals that are chlorinated, containing chlorine, that are used to wash and clean heavy duty stains that water can’t. They’re very volatile and tend to be included in many domestic, commercial, and industrial activities.

They’re mire harmful the more chlorinated it is. Former practises would directly pour spent/used solvrnt directly on dry ground which would then seep and contaminate groundwater.

Many of them are being phased out as we gain a better understanding of them and their effects.

Classical Sources of Contaminants

The classical source of air pollution tends to be the combustion of various materials which then emits various chemicals.

Some examples include waste burning, wood burning, incinerators, car exhausts, coal power plants, and many more.

Winter Smog

Is often considered the deadliest form of air pollution and occurs from anthropgenic combustion & other activities.

It is mainly compased of PAHs that have very small particles (P10, P2.5) They’re also made of SO2, NOx, CO, mineral dust, organic matter, and soot. Chemicals in the smog tend to be carcinogens that can penetrate deep into the lungs and bloodstream unfiltered.

PAHs

Polycyclic aromatic hydrocarbons (PAHs) are a large fanily of compounds composed of benzene (C6H6) rings. Typically, the more benzene rings they have, the more toxic they are. Some are carinogenic, mutagenic, and teratogenic.

They’re the most widespread organic pollutants. However they are naturally occuring from crude oil and coal. But anthropogenic activities have exacerbated them, mainly the imcomplete combustion of carbon containing fuels.

Summer/Photochemical Smog

Occurs when UV light is absorbed by and reacts with hydrocarbons and nitrogen oxides, which typically comes from car engines. This results with various air pollutants including ozone, nitric acid, and PAN.

These pollutants tend to be extreme eye and respiratory irritants.

Temperature Inversion

The main driver for summer smog. It’s essentially when the normal regime of warm air near the surface and cooler air above reverses due to geographical topological structures such as a mountains and valleys.

This causes stagnation, preventing air pollutants from rising and dispersing and instead building up.

Stokholm Convention

An international treaty that aimed to ban and restrict the production and use of 12 POPs referred to as the ‘dirty dozen’. It was first talked about by the UN in 1995, signed in 2001, and made effective in 2004.

Despite the widespread ban of POPs in the 70s, it was clear that more attention and action was required.

The dirty dozen were split into three main groups:

• Organochlorine Pesticides: synthetically produced to deal with pests

• Unintentional Byproducts: came about from the use of other chemicals

• Industrial Chemicals: synthesised artificially for various uses.

While although a lot of these chemicals were phased out, we also have to recognise how they did have a beneficial effect as well. When phasing out chemicals, we’d also have to think of the benefits these chemicals and how realistic it is to phase them out (is it point or diffuse source, etc)

Either way, the persistence of thede chemicals means that they are still present and distributing in our environments globally despite the reduced emissions and controlled sources.

POPs

Persistent organic pollutants (POPs), a cateogry of chemicals that resist chemical, biological, and photolytic degradation.

This typically means they have the capacity to bioaccumulate and have long range transport, potentially even globally.

This global distribution is typically done through global wind currents, circulating through various systems and spheres, and is known as the grasshopper effect.

DDTs

Dichlorodiphenyltrichloroethane (DDT) were widely used as an insecticide back in the day. Was first synthesised in 1874, but first used for its insecticidal properties during WWII to control mosquitoes and lice. Production of it increased afterwards.

Rachel Carlson described and observed effects of DDTs in bird populations and talked about possible human effects of it in her book ‘Silent Spring’.

Arounds the 70s-80s, agricultural use of DDT was widely banned and it was banned worldwide in 2001 with the Stockholm Convention. However, it is still widely used in disease vector control.

Dioxins & Furans

The byproducts of when chlorine and organic matter and burnt together at very high temperatures.

They are naturally occuring in forests fire. But, most of it comes from anthropogenic combustion (residential, open-waste burning, wood preservation, incernerators, and so on)

PCBs

Polychlorinated biphenyls (PCBs) are very stable compounds that have low vapour pressure and high dielectric constants. These chemicals had many applications, mainly being industrial such as in building materials, fire retardents, coolants, and so on.

As a POPs, it had the ability to disperse and bioaccumulate globally. It has been observed in sediments and animal tissues all around the world.

It has carcinogenic, eye irritiation, decreased birth weights, dermal lessions, and diverse hepatic effects. PCBs commonly occur in mixtures of other compounds whose effects aren’t fully understood yet.