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Lectures 5 - 6

Terms in this set (57)

Lecture 5: Contaminants in the environment. Environmental fate
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Now we know....
• Multiple sources of contamination in soil, air and water:
• Legacy contaminants: Emerging contaminants:
• Many contaminants can be toxic Types of effects:
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Question: Can you cite ..

1. 3 legacy contaminants
2. 3 emerging contaminants
3. 3 types of negative effects
3 legacy contaminants
- PCB's
- DDT'S
- Dioxins

3 emerging contaminants
- "Down the drain chemicals"
- Microplastics
- Pharmaceuticals
- PCP's

3 types of negative effects
- Endocrine disruptors
In this lecture, we're going to talk about the effects of these contaminants once released into the atmosphere, its environmental fate: in soil, air and water.
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Like eco-toxicity, there are many scales that we may be interested in.

What are 4 of these scales and what do they encompass?
Soil aggregate: How soil compounds come to stick to soil aggregates

Through soil profile: How much of a compound like pesticides may be leaching down into the ground water.

Catchment scale: Scientists and stakeholders may be interested in this at a larger scale like water production companies who want to understand the processes of a catchment scale

Long range transport: Persistent organic pollution (POPs) and the Stockholm conversion, we realise that we need to understand long-range transport or global transport throughout the earth

One doesn't exclude the other, instead they are described as different equations, processes and kinetics, but their all important for different purposes.
After their emission, organic contaminants will undergo the three stages of distribution, transformation/degradation and transport.

What occurs in each of these stages?
1. Distribution of these compounds between different phases: Each environmental compartment = several phases

2. Transformation/ degradation by
chemical/biological reactions

3. Transport within and between compartment(s)

(1, 2 and 3 occur simultaneously and can influence each other which creates a very thin or challenging situation according to the day)
First we will discuss the first stage of distribution between different phases.

We are going to use the example of cooking pasta or rice. What is the processes occurring during this cooking time?
• The system is made of 3 phases
• The chemical will distribute/partition between 3 phases according to its chemical properties
• There are changes between the stages going from a solid (pasta) to a liquid (water) then to a gas (air). These are all interchangeable.
Following with the pasta example, what will happen to contaminant in this system?
- Interact with the pasta (absorbing)
- The compound will go from the water to inside the pasta or into the air after dissolving.
- There may also be other interactions with other chemicals or micro-organisms.

Depending on the chemical, it will distribute or partition among these 3 phases. Some may accumulate in these different stages.
We can find the partitioning co-efficient by calculating the ratio of the concentration of chemicals in phase 1 and 2.
It may take a couple of minutes for the compound to distribute and reach an equilibrium.

Then we can talk some of the pasta, determine how much the compound is in there, take some water and determine how much of the compound is in there, make the ratio between these two concentrations (which is represent din the image) in phase 1 (pasta) and phase 2 (water).
What does the partitioning coefficient ratio tell us?
• The higher the K1,2 coefficient, the more chemical accumulates in the phase 1 (pasta) relative to phase 2 (water)
The smaller it is, the more chemicals that remain in the water
• K1,2 is specific to the chemical and the type of pasta

These co-efficients depend on the chemical and pasta properties. So if your cooking peas, perhaps the compound isn't going to partition so much into the solid if your cooking pasta.

So we need to calculate these for all the chemicals in the environment which is a lot of work.
What did we realise after years and years of measuring these partitioning co-efficients?
We may represent the environment in a simplified way, considering ideal phases. We consider liquid, gas and the solid phases. After measuring the partitioning of contaminants into lots of things like fish, leaves, soils snd sediments, we realise that there's fraction of loose solid phases that play a great role into this partitioning.

It's apart of the organic matter that can be represented by a surrogate that is octanol/water.
While trying to simplify our environment by trying to find something that will make it easy to measure in the lab, we come across octanol (Kow)

What is the octanol/water partitioning co-efficient?
- It has the same ratio for C and O like fatty acids and lipids
> a surrogate of organic phases in the environment

They tend to accumulate in the fats (or lipids bilayers of walls of cells).

In the picture, their investigating the partitioning of a green dye (that remains in the water). If we measure the conc. of the compound in the octanol and divided it by the conc. of the water, we'd have very small Kow (depends on the compound).

We can use this Kow as something to hep compare different compounds.
Here's an exercise to better understand the octanol/water partitioning co-efficient.
The equation you need to remember is

Kow = Coctanol/Cwater
- Its 10 because it the conc. of the compound in octanol seperate to water (there's 10 in octanol A and 1 in water A)

Which chemical is likely to accumulate in pasta/soil/organisms?
- Compound A
- This is because the higher the Kow, the higher the the tendency of the compound to accumulate because octanol is a surrogate for fat, oil and lipids etc. so A will accumulate much more in a solid matter compared to B which tends to end up in the water.
How does the previous question relate to the environmental fate of contaminants?
Because compound A, the dense one, will end up in your foods, milk, butter, and eggs etc.

However B is in water so you may be exposed to this in your drinking water.

So a simple text in the lab can tell us where the compound is going to accumulate and which route is going to lead to a receptor, terrestrial or sedimentary organisms etc.
If we look at the Kow for DDT (insecticides), what can we see?
DDT bio-accumulates in organisms and the food chain and has a log Kow of 6.4.

This means that Coctanol is found one million times higher than it's Cwater. Therefore, DDT is not found in water.

Theres a strong negative relationship between Kow and water solubility so the more hydrophobic, the less soluble it is in water and that is what the graph in the image shows.

SO, SOLUBLE COMPOUNDS WIL HAVE A SMALL KOW
Many distribution coefficients to environmental solids are proportional to Kow.

Another reason for calculating partition ratios is to predict bio concentration factors, how much will accumulate in a fish.

What does it tell us?
The higher the KOW of a compound, the more hydrophobic, the higher its tendency to partition in solid phases (OM, biota etc...)
Now we are going to look at the transformation/degradation stage (by chemical/biological reactions) that organic contaminations undergo after their emission. This doesn't really apply to inorganic compounds like metals that don't degrade.
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Give a definition of transformation
All reactions in which chemical bonds are broken/formed (sometime micro-organisms add stuff to our contaminants that changes its properties and toxicity).
Give a definition of mineralisation
Often, micro-organisms will eat up bits of our contaminants up to a point where we can't recognise the initial structure of our original contaminant. This is called mineralisation.

All the bonds are broken down and the products of those transformation or chemical reactions are mineral products such as CO2, Ch4, H2O and SO42-.
Give a definition of detoxification
In many cases when you have a product that is transformed, broken or something has been added on it, its toxicity is going to be reduced. They've been designed in such a way they their bio-activities are maximal to some extent.

Products are less harmful
Give a definition of activation
In some cases, the transformation of of contaminants end up in the production of metabolites, product of degradation, that are more toxic. This is tricky to deal with.

Diagram: In the environment under certain conditions, the bonds between C and Cl can be broken down to produce Vinyl Chloride Carcinogenic metabolite, a metabolite from the product of transformation.

We don't want this degradation to occur and stop here as it may result in something that's super toxic.

Products are more toxic than the parent
Degradation is good in some cases but we have to make suer that this process is complete with the mineralisation of compounds in organic compounds otherwise we risk to having something that's more toxic than the parent compounds.
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Theres a great variety of possible reactions in the transformation process (adding or removing bonds) that can be divided into what categories?
Abiotic and biotic
What are involved in these abiotic and biotic catagories.
ABIOTIC:
- No direct participation of organisms
> Chemical reactions (in the dark) and photolysis (solar radiation) as light exposure can break their bonds.

BIOTIC: Were mostly interested in these in envsci
- Biologically mediated
> Rate is generally much higher
> Only processes by which, complete mineralisation can be achieved
> Biodegradation leading to mineralisation can be a good thing when you want to get rid of contaminants.
Another distinction we may want to make are those redox reactions with an exchange of electrons.
Red‐ox:
e‐ transferred from (oxidation) or to the contaminant (reduction)

No e‐ transfer:
ex: hydrolysis

Most of the contaminants that were looking at, occur by redox reactions. If a contaminant can fit into this scheme, it is like to be biodegradable as organisms can gain some energy from it.
What are the requirements for biodegradation?
1. Existence of organisms with degradation potential. They need the right enzymes to break down these bonds. Essentially, every contaminant is biodegradable. However, one or more of these criteria may be missing which explains why it isn't biodegradable.

2. Presence of specific degrader(s). Evolution tells us that if an organism only has one contaminant to feed one they can develop to capacity to degrade it. Its useful to engineer organisms to break down specific contaminants that aren't usually biodegradable.

3. Accessibility of target pollutants

4. Induction of appropriate degradative enzymes

5. Availability of appropriate e‐ acceptors/donors

6. Availability of nutrients

7. Adequate pH and buffering capacity

8. Adequate temperature

9. Absence of toxic or inhibitory substances
How fast will a contaminant degrade in the environment?

It is complicated and it depends... Can one number be used to compare compounds and/or different environments?
The image shows how complex the insecticide of Parathion that has been studied and the metabolites it breaks down into. As you can see, it is very complicated.

To answer this question there are many questions to address..
• One or several transformation pathways?
• What are the metabolites?
• What are the kinetics of the different reactions?
• What is the resultant elimination rate?
• What is the influence of environmental variables?

Eg: temperature, pH, light intensity, redox condition, ionic strength, presence of certain solutes, concentration and type of solids, microbial activity...
We have designed some tests in the lab that simplify processes like the degradation of Parathion, a bit like eco-tox.

To understand the effect of a contaminant once emitted into the atmosphere and compare different compounds, we can use the DT50: half life test.

How is this carried out?
This example is based on soil degradation but can be applied to water, sediment etc.

We have 4 different soils that are live with lots of micro-organisms. You add your chemical to each of the soils then incubate these samples at a constant temper, moisture content and in the dark (controlled). Over time, samples are taken regularly and analysed for the concentration of chemical remaining.

Then you create a degradation curve showing the concentration remaining and time. A t=0, there is 100% of the compound, and over-time micro-orgimsms are eating away at the compounds. Eventually, you'll arrive close to 0 (may take some time). From the curve, you can track point DT50, called the "half-life". Its the time required for 50% of the conc. to be degraded.

From the graph in the image, we can see that compound red is most degradable. This is good as this can measure persistence but we must consider, how long can we tolerate compounds in our environment?

This shows how extreme DDTs are as their DT50 is around 30 years.
Now we're finally onto the last stage of transport, on what happens to organic contaminants after their emitted.

We'll look at the fate of chemicals in soil profile. To help understand this, we''ll look at pesticides as they're right onto in our crops.
Look at the diagram to see the different zones in the soil.

The blue arrows represents the movement of water from the top soil and the ground water though leaching. We also have horizontal pathways, overland flow, like run-off n the surface, sublateral flow, including drains and finally the ground-water recharge between ground-water and surface waters.

We can see the three phases (from the first distribution phase). When the compound is applied on top of the field (input of chemical), it will partition into the solid, liquid and gaseous phases and can stick to the soil on the surface. Because it is volatile, it can escape back into the atmosphere and be dispersed. IN the liquid phase, plants can uptake it (bio-available), it can be degraded and it can move together with the water.

If it remains in the solid phase it'll be mobile and micr-organisms cannot degrade it and it'll accumulate there. Continuously applying pesticides will cause its accumulation in large frequencies, which is why happened to DDT. Since its been there since the 50's it's had time to very slowly distribute all over the place.
Now ee'll look at the fate of chemicals in surface water bodies.
In the diagram we have sediment below, sediment suspension, some plants and organisms living in the water column. We have to consider water inputs and outputs moving upstream or downstream, groundwater inputs (that may come with contaminants), run-off and erosion (coming from the fields with lots of pesticides), sewage plant discharge and untreated waters. These are most of the inputs of water and contaminants coming into surface waters.

First, the chemical will dissolve into the water and then its going to distribute between different phases. Volatilisation, and absorption to the solid phases etc. (so distribution and partitioning). What remains is going to move with the water.

Now we may have some degradation occurring via hydrolysis, photolysis and mostly biodegradation and degradation in the sediments. This is going to breakdown and hopefully mineralise the compounds
Key points from the lecture:

1. Chemicals distribute between liquid (water), gas (air) and solid phases

2. Partitioning constants (Kow, Henry's) specific to the chemical.

3. The higher the KOW the higher its tendency to partition into solid phases (OM, biota etc...)

4. Biodegradation can completely eliminate (mineralize) organic contaminants, but it requires many favourable conditions

5. Contaminants distribute, degrade, transport simultaneously, so they are not easy to track.
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Focusing questions:

1. What is the first process occurring after contaminants are released in the environment?

2. What are the most important partitioning constants and what are they used for?

3. What are the main degradation mechanisms for organic contaminants?

4. What is a metabolite and why should we worry about?

5. What happens to contaminants once they are released in surface
water?

6. What happens to contaminants once they are released in soil?
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Lecture 6: Solutions
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Should we do something about it and why?
Yeah bro.

Resources to do this art very limited as it takes a lot of time and money. We also have human visions, so our priorities or what's important to us often changes as well.
Why is there a really strong emphasis on groundwater protection?
70% of the Earth is covered by water. However, 97% has high concentration of saline thus making it unsuitable for drinking and salivating this water is an expensive process.

Out of the 3% of freshwater remaining, 68.7% of it are icecaps and glaciers with the following 0.9% being ground water and 0.3% of it being surface waters. Out of this 0.3%, 87% are lakes, 11% are swamps and 2% are rivers.

Basically, ground water represents ~ 99% of available fresh water so its essential to protect it!
Fact: In NZ: nearly 40% of the community drinking water supply from GW (+ many individual rural household) so it is essential to protect it.
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Give 3 reasons why soil is so important to protect.
Receives large quantities of pollutants:
> Ex: leaking storage tanks, chemical spills, landfill leachates, atmospheric deposition, illegal disposal etc...

Serves many ecosystem functions: Including growing our food

Soil = Filter preventing contamination of GW by sequestration (sorption) and/or detoxification (degradation). They also contain many micro organisms that are helpful for breaking down some contaminants.

There's a lot of potential to degrade many contaminants and decontaminate the contaminants.
What can we do about (organic) pollutants?
What is remediation?
Reversing or stopping environmental damage
What is the traditional approach to remediation for legacy contaminants?
DIG & DUMP

1. Soil excavation:
You have contaminated soil the you dig up and put it somewhere else where it wont affect something of value. This is very labour/energy intensive and exposure when soil is transported is
not always successful

You can do something similar with water.

2. Water pumping:
You pump up the water and put it somewhere else where it wont affect something of value. Is quite basic and very labour and energy intensive. You may also miss the point where the contaminants are
How do alternative approaches take advantage of the contaminant properties to remediate it in a smarter way?
Transfer the contaminants from one phase to another (remember those useful constants?)
> high Kow: easily transfer from water to sludge/activated carbon. If we have a compound with a very high Kow partitioning coefficient, this means that they will have the tendency to stick to solids. If we know how these compounds react then we can use another compound that the compound likes to stick to to get it off the solid.
> high Henry constant: describes the transfer from water in to the air from something that is a volatile into a gaseous phase. Perhaps we can bubble some air into the water to collect these contaminants into the air phase and your water is cleaned up.

Degradation: create favourable conditions for biodegradation or abiotic degradation. We'll have to figure out what factors are missing and modify the environment.
Give 4 more examples of alternative/innovative approaches to remediate organic pollutants.
1. Compost/bio-pile
- this provides bugs and microorganisms with favour environments to be able to breakdown contaminants.

2. In situ Redox manipulation
- in many cases degradation is not occurring due to the lack of transfer of electrons which is the reason why biodegradation is not happening. So here we have a plume, and some pipes going underground that delivers electron donors and acceptors so the right conditions are available for these compounds to degrade and we can get clean consumable water.

3. Reactive barriers
- We start off with highly contaminated GW (point source of chlorinated solvents or BTEX). We then build a big trench/barrier that we we fill with material. This can be activated C so that the compound absorbs onto the material so what comes out of the barrier is clean water. There'll also be some micro-organisms or materials that will change the redox conditions that enables degradation. We can then create fencer barriers that will take advantage of the transfer from one phase to the other.

4. Soil vapour extraction
- these are often implemented for chlorinated solvents. These are very volatile and will easily transfer from water into the gaseous phase. At the bottom we have water and chlorinated solvents underneath former dry cleaners. Again, we can engineer this environment and makes some holes and pipes that will bubble some air that will make the chlorinate solvents move from water to the gaseous phase. Then we can recover it and make it interact with a solvent so it can stick to a solid phase and will now concentrate into this area where this now clean air will be released nearby. This os often used in Europe. It's basically moving compounds from one phase to another.
A famous remediation projects includes PCBs in the Hudson River (NY State, US).

How they did they undergo this remediation project?
1947-1977: two capacitor manufacturing plants released 590 000 kg of PCBs. 10ppm in sediments (1-2 orders of magnitude > typical concentrations)

1976: fishing was banned as thy were very toxic to consume.

Many programs of remediation work since. One of the largest and most complex clean-up project in US history

1978: 140 000 m3 of sediments removed

2002: decision to remove more, based on 50 000 samples

2009-2015: dredging 24/7 for 6 months/ year for 6 years.
> 1.5 million m3 removed. These were transported by boat, truck, train
> Size separation: gravel, sand removed.
> finer fraction (most contaminated) dewatered > cake > landfill > water: treated, discharged
What activities can we undergo for contaminants that we are currently producing?
Mitigation Monitoring
Find alternatives
This a a map showing the number of studies detecting one or more pharmaceuticals.
Some of these countries in white are due to the fact that there had been poor analysis of contaminants present in the country.
Monitoring. We can only find what we look for.

What kind of monitoring techniques are there?
Sewage treatment plant effluent/ influent, surface water, soil, air (indoor,
outdoor), sediments, biota etc...
What are the challenges of monitoring?
Analytical challenges: 1 sample = several hours of preparation

Budget challenges: 1 sample = several NZ$100 to prepare and analyze

MONEY! ITS EXPENSIVE!
Where and when do we decide to sample for contaminants?
High spatial and temporal variations.

- Need samples that will represent the presence of contaminants as accurately as possible
Sewage treatment is controlling the release of down the drain chemicals into rivers/seas and NZ's harbours as well.
We have this plant that is cleaning sewage water but they aren't designed to clean/treat all the organic contaminants that we've been learning about. Its mainly been used to treat micro-organisms and nutrients.
Concentrations and removal of pharmaceuticals in sewage treatment plants in different countries.
This is an example that measured the conc. of antibiotics of when they enter and exit these sewage plants.
> great variability for a given compound
> If we start with a high number and sendup with a low number, this means that the removal rate has been very high (we can see this in the table here
> The removal of organic contaminants in sewage treatment plants is dependant on many factors and they aren't always controlled.
What can we do about future contaminants?
Risk assessment and Regulation

There are many things we need to consider in the future when industries are proposing to release new compounds in the environment.

We also have to ensure that these compounds are worse than the existing compounds that are phasing out.
Regulations and restrictions.

The Montreal Protocol is another international convention that is extremely successful.

If we don't use and consume contaminants then they aren't related into the environment.
CFCs, chloroformed fluorinated carbons (responsible for ozone layer destruction) are very small molecules that were used in sprays that were phased out by the Montreal Protocol (1987) and were replaced by organic compounds that are degraded before they reach the stratosphere.

Other examples: more POPs in the Stockholm Convention, restriction of microbeads and antibacterial substances in PCPs, toxic pesticides etc...
Whats an issue with POPs and PCPs?
They don't degrade. So they don't become future or present contaminants. They just remain as legacies.
We use risk assessment to help make these decisions.

What exactly is this?
RISK = EXPOSURE X HAZARD
term-55
Risk is the product of exposure and we can use this for human and ecological risk assessment

• Applied to many substances before they are placed on the market: e.g.
pesticides, pharmaceuticals
• Is the risk acceptable?
• We need to know:
> The sources
> What happens
> How much is where?
> How toxic?
> From this we can determine how they're going to distribute, degrade and where their going to end up.
By comparing what you find in the environment and what you think is terrible, you can determine your risk.

If you have very high exposure to something that is very toxic, the risk is very high. If you have a substance that is highly toxic, but isn't going to be related and stays in the lab, there's no risk for it in the environment.
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To conclude:

• Don't forget: the situation is much better than 50 years ago
Ex: The Thames was dead. Air quality in cities has greatly improved. More people have access to high quality drinking water. Successful global conventions (Stockholm , Montreal etc).

• We can see many emerging contaminants we did not see before

• Our use of novel and unnecessary chemicals tends to increase.

• Take action! Good science helps making good decisions.

• Scientists, policy makers, industry, consumers
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Focusing questions:

1. What are the main actions that can be taken about legacy, present and future contaminants?

2. Why is it important to protect the aquatic and terrestrial environment from contamination?

3. What are the two main principles used when remediating organic contaminants?
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