Science in the box

Quantitative Structure Property Relationships (QSPRs), help environmental fate scientists to initially understand how a chemical’s properties behave in different environmental compartments. From this starting point, models for predicting a molecule’s environmental fate can be made, speeding up the risk assessment process.

Most wastewater goes to wastewater treatment plants where fate processes act on the ingredients. After treatment, some of the product ingredients may reach the environment. The environment consists of the soil, water, groundwater, sediment and atmospheric compartments. To predict which compartment our ingredients end up in, we use QSPRs to understand how a chemical behaves (i.e., its chemical properties), fate processes to generate data or to refine the data from the QSPR, and environmental fate models to predict where the chemical will end up. We use monitoring studies to verify the prediction made by the models so we can use models for future predictions with more confidence.

The first step in estimating chemical properties is often to use a Quantitative Structure Property Relationship (QSPR). Every molecule has many different chemical properties. These properties include things like solubility in water, volatility (how quickly the molecule evaporates), the boiling and melting point and the solubility of the molecule in fat. Each of these properties tells the fate scientists something about how the chemical will act in the environment or in an animal. QSPRs help scientists understand whether a compound is likely to bioconcentrate in fish, biodegrade and be converted to CO2, etc. From any one property, it is difficult to fully understand what will happen to a chemical in the environment. To get a full understanding of where an ingredient goes in the environment, many chemical properties are used with environmental fate models. If environmental behaviour can be predicted with equations, the process of risk assessment can be greatly sped up.

In some cases, QSPRs alone do not provide sufficient data to accurately estimate environmental concentrations. When this occurs, environmental fate testing is conducted.

There are four main environmental fate processes: biodegradation, volatilization, sorption and dilution. P&G’s environmental fate scientists conduct various tests to ensure that our ingredients have minimal adverse effects on the environment and animals. Whether a consumer product ingredient is found in the sewer, a wastewater treatment plant, river water or soil, the same treatment, or fate processes act on these compounds to reduce their concentration in the environment. These four major treatment processes are biodegradation , volatilization , sorption and dilution .

All of these fate processes act together to reduce the concentration of consumer product ingredients in the environment. We work to understand these processes to improve our ability to:

• Better understand the environment,
• Design environmentally friendly compounds, and
• Better predict the concentration of our ingredients in the environment.

Our efforts to understand what happens to our materials in the environment start with the prediction of biodegradation, volatilization and sorption using a Quantitative Structure Property Relationship (QSPR) . These predicted values are used in computer fate models to predict the concentration of our ingredients in surface waters and soils around the world. For those compounds for which QSPRs do not provide good estimates of fate processes, we conduct a series of laboratory tests. The results of these tests are then used with the fate models to predict environmental concentrations.

To make sure that P&G's ingredients do not affect crops or organisms living in soil, we use fate models to predict concentrations in sludge. The key is to understand if concentrations are below levels causing adverse effects to these species. The process we use to compare fate and effects is called environmental risk assessment.

Understanding the Role of Bacteria
Biodegradation (the process where bacteria get energy and nutrients while breaking down a chemical) is the most important environmental fate process as it results in the elimination of the ingredient from the environment.
Bacteria have evolved over millions of years to be able to get energy and nutrients from chemicals in a process called biodegradation. Bacteria grow by breaking down chemicals into smaller compounds, nutrients and water. With the nutrients and energy produced, more bacteria are formed. Since many ingredients are made up mostly of carbon atoms, bacteria may be able to convert that ingredient into CO2, water and nutrients.

When this occurs, the ingredient does not pose a risk to the environment because CO2, water and nutrients are safe. When biodegradation is incomplete, molecules which are smaller than the original ingredient are formed. These new molecules are called metabolites and are intensively studied by fate and effects scientists.

Of all the fate processes affecting consumer product ingredients, biodegradation is the most important because it results in the elimination of the ingredient. If the ingredient no longer exists, there is no concern about its potential to affect the environment. Hence, we spend a lot of time studying biodegradation.

Biodegradation Tests:
There are a number of different biodegradation tests, ranging in complexity from the simple Ready Biodegradability Test to the more complex Porous Pot Test and the Anaerobic Biodegradation Test. As in toxicity testing, environmental fate scientists start with the simple tests (Ready Biodegradability Test) and progress to the more complex tests as needed.

The Ready Biodegradability Test









When a chemical compound biodegrades, CO2 is produced. The Ready Biodegradability Test measures the rate of bacterial performance during biodegradation by the amount of CO2 emitted in the Electrolytic Respirometer.

Set-Up
The Ready Biodegradability Test uses microorganisms obtained from a wastewater treatment plant. These organisms are put into glass jars with the test compound for 28 days, and carbon dioxide (CO2) gas is measured in the air above the test solution. If the compound biodegrades, CO2 will be detected. The more CO2 produced, the greater the biodegradation of the test compound. This simple test has been highly automated in P&G laboratories and is usually conducted on an instrument called an electrolytic respirometer, which automatically measures the CO2 produced by the bacteria.
In this test, the concentration of the tested chemical is very high and the number of bacteria very small compared to what can be found in a wastewater treatment plant (only a few drops coming from a wastewater treatment plant are added to litres of testing media). If, under such difficult conditions, the ingredient degrades, it is expected that it will degrade very well in the natural environment.

International Compliance
This test is used to comply with most worldwide regulatory requirements to ensure that new chemicals put on the market are biodegradable (or safe when a full risk assessment is conducted). In the EU, for example, the requirement is that more than 60% of CO2 must be produced in a time period of 10 days (after the degradation has reached at least 10%). All the surfactants we use in our detergents meet this criterion. (See ingredient safety information on this site.)

Acclimation and Lag Phases

This test uses a dilute microbial inoculum which has never been exposed to the test compound before. This means that if the chemical is new (newly created by chemists), the bacteria will need first to synthesize the necessary enzymes before degradation can start. This is called the acclimation phase and can be observed in the graph. The tested chemical is introduced in a flask where the bacteria had never seen the chemical before (blue line) and in a flask where bacteria had first been exposed to the chemical in a separate chamber (red line).
The lag phase between Days 0 and 5 for the blue line indicates that the non-acclimated bacteria needed up to 5 days to produce this new enzyme, allowing the bacteria to start using the carbon in the molecule as a food source.
When a Ready Biodegradability Test is conducted, there is always a control flask that contains a rapidly biodegradable substance (glucose, for example) to ensure that the bacteria taken in the wastewater treatment plant are still alive. The biodegradation profile of this substance is shown by the black line.

Porous Pot and Continuous Activated Sludge Test Systems









Porous pots are laboratory scale of wastewater plants. They enable a longer duration test of a compound’s biodegradation and whether it will end up in sludge.
Using Sludge
The Ready Biodegradation Test helps us understand if a material may degrade during wastewater treatment and in the environment. However, this test uses very high concentrations of test compounds, which are very often not realistic. To better understand the potential for biodegradation, we frequently use the more sophisticated Porous Pot Test.

In this test, activated sludge from a wastewater treatment plant is brought into the laboratory and exposed to the ingredient for weeks or months at a time. The long duration of testing allows acclimation of the microorganisms to occur.

We typically use a radio-labelled test compound that allows us to use very low concentrations of our ingredient and get a good understanding whether the compound will degrade during wastewater treatment and in the environment. Since the porous pots are laboratory scale models of wastewater treatment plants, they provide excellent data on whether a compound will biodegrade and exactly how fast that will occur. Furthermore, we can measure sorption and learn how much of the ingredient will end up on sludge.

Anaerobic Biodegradation Test





Some bacteria can live without oxygen (anaerobic bacteria). It is important to test situations where bacteria can biodegrade in environments without oxygen (sediment in streams, some situations in wastewater plants).

Testing in Anaerobic Situations
The Ready Biodegradability Test and the Porous Pot Tests look at biodegradation in the presence of oxygen (aerobic). However, there are some situations where oxygen is not present but anaerobic bacteria (bacteria which live without oxygen) can still degrade detergent ingredients.
The sediments of some streams and the anaerobic digesters of some wastewater treatment plants are two locations which lack oxygen, but where detergent ingredients can be found. Since it is important for us to study the degradation of our materials wherever they exist, we also study biodegradation in anaerobic situations.

Volatilization is the process of evaporation from the wastewater.

The other major process that occurs during wastewater treatment is sorption to sludge. Sorption is the process in which a chemical sticks to a solid surface such as a clay or soil particle, bacteria or some other particle in the wastewater to form sludge.

Sludge is composed of bacteria that grow in wastewater treatment plants. Many ingredients will stick, or adsorb, onto sludge. During wastewater treatment, sludge and the sorbed ingredients are removed.
Sludge can be disposed of in a number of ways, including landfill, incineration and application to farm fields. Application to farm fields helps to reduce the need to landfill or incinerate this waste and provides a service to the farmer, since sludge is an excellent fertilizer.

Clearly, on average, small wastewater treatment plants on large rivers have a much larger dilution factor than large wastewater treatment plants on small rivers. But what happens as river flow is reduced during a drought or just during the dry part of the year? Rainfall has a huge impact on river flow that can dramatically influence the dilution factor. Hence, the simple process of understanding dilution becomes very complex.

The information from initial fate research is combined with measured fate data and with the amount of the ingredient sold. Then a computer based fate model predicts the concentrations of our ingredients in each environmental compartment (river water, river sediment, sludge amended agricultural soil, groundwater, air). To ensure that these models are accurate, the results are often compared with measured environmental concentrations determined during monitoring studies.