Science in the box

These Life Cycle Impact Assessment categories are what we consider "indicators." Indicators are unlike quantitative inventory data that measure weights of materials or emissions and consumption of energy or heat content. Indicators are conversions of these inventory data.

It is important to understand both the advantages and limitations of the conversion in order to interpret the indicators properly and reach sound conclusions.

Most indicators are "directional" to a greater or lesser degree. P&G is cautious to keep in mind that the use of numbers for the value of an indicator may incorrectly imply that it is quantitative and that any differences are absolute and meaningful.

This is not true in all cases. Indicators differ widely in how they relate to the environment and the assumptions used to derive them. In all cases, the assumptions may not be fully scientific. Some indicators take on the nature of judgmental scores or even opinions.

In a Life Cycle Impact Assessment (LCIA), essentially two methods are followed: problem-oriented methods (mid points) and damage-oriented methods (end points).

In the problem-oriented approaches, life cycle inventory flows are classified into environmental effects. Mid points covered in most Life Cycle Assessment (LCA) studies are: Greenhouse effect (or climate change), Natural resource depletion, Stratospheric ozone depletion, Acidification, Photochemical ozone creation, Eutrophication, Human toxicity and Aquatic toxicity. These methods aim at simplifying the complexity of hundreds of flows into a few environmental areas of interest. The EDIP or CML 2000 methods are examples of problem-oriented methods. They are generally easier to understand, but can still lead to a considerable number of indicators from which it is difficult to support a decision.

The damage-oriented methods also start by classifying a system's flows into various environmental themes, but model each environmental theme's damage to human health, ecosystem health or damage to resources. For example, acidification - often related to acid rain - may cause damage to ecosystems (e.g., in the Black Forest in Germany), but also to buildings or monuments. In essence, this method aims to answer the question: Why should we worry about climate change or ozone depletion? EcoIndicator 99 is an example of a damage-oriented method. Because there are only 3 types of damages, it is easier to come to a conclusion. The downside is the interpretation/communication of the result (see further).

Problem-oriented methodologies are based on internationally and scientifically accepted approaches when possible. But some categories, such as human toxicity or aquatic toxicity, remain difficult to model and are currently under development and require careful evaluation when used. There are even more difficulties with scientific relevance with damage-oriented methods, hence careful evaluation is necessary.

An important issue with problem-oriented methodologies is the communication aspect of the results. For example, the human health indicator for EcoIndicator 99 uses the concept of "Disability Adjusted Life Years (DALY)." When assessing the life cycle of drinking water production, how do you communicate that producing drinking water constitutes a certain number of Disability Adjusted Life Years?

The earth's climate is driven by the balance of energy or heat added by the sun and lost by the earth. The primary energy is lost through heat radiation, much like the heat you feel coming from a stove. Several gases in the atmosphere, called greenhouse gases, can reflect some of this heat back to the earth. This effectively warms the earth and may alter the climate over time as these gases increase in concentration.

A greenhouse gas indicator is derived from two basic properties of each gas. The first is its ability to reflect heat. The second is how long the gas remains in the atmosphere, that is, how long it may act to reflect heat. These properties are then compared to the properties of carbon dioxide and converted into carbon dioxide equivalents. Then the individual equivalents are added together, for the overall greenhouse gas indicator score that represents the total quantity of greenhouse gases released. Most of the methods used in Life Cycle Impact Assessment (LCIA) are based on those developed by the Intergovernmental Panel on Climate Change (IPCC).

To interpret the greenhouse gas indicator, an important variable is the time horizon used (e.g., 50 or 500 years). Most greenhouse gas protocols work with 100 year time horizons.

High in the earth's stratosphere, chemical processes maintain a balanced concentration of ozone. This protects the earth by absorbing much of the harmful ultraviolet radiation from the sun.

If a gas carrying bromine or chlorine atoms can stay in the atmosphere long enough to reach the stratosphere, the ozone balance may be threatened as free bromine and chlorine can accelerate the breakdown of ozone. This is especially true when bromine and chlorine are on the surface of tiny ice crystals and sunlight catalyzes the reaction.

The ice crystals may form at the Arctic and Antarctic poles during their winters, when sunlight does not reach them. When sunlight first reaches them in the spring, ozone holes may be created for about a month before the crystals melt and the ozone is regenerated.

An ozone depletion indicator is derived through several properties of a gas. These include its stability to reach the stratosphere and the amount of bromine or chlorine the gas carries. These properties are then compared to CFC-11, a once common refrigerant*. The properties of each gas are then compared to the properties of CFC-11 and converted into CFC-11 equivalents. Then the individual equivalents are added together for the overall ozone depletion indicator score, which represents the total quantity of ozone depleting gases released.

*Although CFC-11 is now banned by the Montreal Protocol in industrialized nations, it is still manufactured in many developing economies.

Natural rain is slightly acidic due to the presence of various acids in the air that are washed out by rain. However, a number of man-made emissions are either acidic or they are converted to acid by processes in the air. Examples of such emissions are sulphur dioxide (which becomes sulphuric acid) and nitrogen oxide (which becomes nitric acid).

As a result, the acidity of rain can be substantially increased. In a number of areas (such as large areas of Sweden), the soil and water have a limited capacity to neutralize these added acids. If water becomes too acidic, an increasing number of aquatic species are harmed. If the soil becomes too acidic, the ability of plants to grow and thrive is harmed. The acidity of each emission is converted into equivalent amounts of sulphur dioxide. All emissions are then added into an overall acidification indicator score that represents the total emission of substances that may form acids.

The growth of aquatic plants and algae gradually fill in freshwater lakes and estuaries over time in a natural process called eutrophication. This process is controlled by low concentrations of certain nutrients (like phosphate and nitrogen) that the plants and algae require to grow.

Usually, phosphorus is the limiting nutrient in freshwater and nitrogen in estuaries and salt water. However, when humans release nutrients like phosphate (agriculture ~50%, human metabolism ~20%, industry ~10%, detergents ~10% and natural erosion ~10%), the process of eutrophication is accelerated. In a worst-case scenario, the excess growth of plants and algae can smother other organisms when they die and begin to decay.

An eutrophication indicator is derived by converting the different chemical forms of phosphorus and nitrogen into a common or equivalent form. Then, the proportion normally found in aquatic algae is used to weight the phosphorus and nitrogen. These values are added into an overall indicator.

To interpret the eutrophication indicator, it is important to realize that the background concentration of the nutrient is the baseline. A similar quantity of added phosphorus at one site may trigger a substantial increase in the level of nutrient, while remaining small at another site. Thus, the actual impact cannot be precisely predicted.

By adding phosphorus, which may affect only fresh waters, and nitrogen, which may affect only saline environments, the connection or relevance of the eutrophication emissions indicator to the environment where it is released is usually lost.

Additional investigations to better understand the environmental meaning of the indicator is needed.

Ground-level ozone is formed by a combination of sun, nitrogen dioxide (NO2) and volatile organic compounds (VOCs). Human activity in urban areas often releases large quantities of organic compounds and at the same time, large amounts of nitrogen oxides (NOX) from combustion, to create electricity and to power cars. In warm temperatures and in sunlight (hence, the name summer smog), these processes generate additional quantities of ozone at ground level.

At ground level (not in the stratosphere), this increase in low levels of natural ozone can harm some plants and may irritate the lining of our lungs. This chemical reaction process of VOCs, NOX, and sunlight is highly complex. The particular chemistry of a VOC, the local concentrations, how high the temperature may be, the wind conditions and other factors are all involved.

The reaction process is "non-linear," meaning that sometimes the NOX concentration will drive the reaction. At other times, it is the VOC that drive the reaction. Various indicators take low, average and high NOX concentrations to calculate an overall score.

A photochemical ozone indicator is derived by finding conversion or reactivity factors for each of the hundreds of possible VOCs. This is then used to convert the many possible inventory VOCs into ethylene equivalents. The interpretation of the photochemical ozone indicator should, however, be done cautiously. As with several other indicators, emissions from different sites are added together.

This results in a total emissions load, and not an understanding of local conditions that actually produce the ozone. Furthermore, general conditions are used rather than local conditions that would typically vary from Stockholm to Barcelona to Munich on a given day.

The systems that produce products and services that we use consume energy and materials. Some are renewable like water, wind power and wood, and some are non-renewable like iron, aluminium and oil (although iron and aluminium can be recycled).

Renewable materials must be managed wisely for sustainable use. The supply of non-renewable materials varies from material to material. Supplies of some materials appear as if they might run out sometime soon, while supplies of other materials can appear to be sufficient for hundreds of years to come.

Natural Resources Indicator
A natural resources indicator is derived by dividing energy and materials into renewable and non-renewable categories. We have not yet come up with a way to measure the sustainability of renewable materials or crops, such as wheat, coffee or palm oil. For non-renewable materials, the estimates for future supplies are based on how much economically recoverable supply appears to exist at the present time. Then, different materials are compared on the basis of the implied scarcity. With efficient material use as a central theme in sustainability, this indicator therefore provides useful information.

Aquatic toxicity and human toxicity are impact categories that are best addressed by a tool such as Environmental Risk Assessments, where calculated or measured concentrations in the environment can be compared to a no-effect concentration.

This is a critical step when assessing whether a chemical is safe for living organisms. Because Life Cycle Assessment reports only aggregate emissions across time and space, no environmental concentration can be calculated. At best the results of these types of indicators point to the life cycle stage with highest needs for further assessment by risk assessment. For aquatic toxicity of detergents, whilst using simple methods, it is clear that the largest contribution comes from the unremoved fraction of detergent chemicals after sewage treatment. This is indeed where the environmental risk assessment is focused, to ensure the use of detergents is safe for the environment.

The current human toxicity models only include exposure models for inhalation and ingestion. However, for the majority of our cleaning products, skin exposure is the most important exposure route. Since the life cycle emissions that contribute through inhalation and ingestion (including indirect exposure) are primarily related to combustion processes, there is usually a strong correlation between energy and human toxicity.

In the past decade, a number of new impact categories have developed. However, many of these new impact categories are highly complicated requiring the need of a separate calculation model for practical implementation. As these models are lacking in most cases, it is impossible to apply them to new products and chemicals.
There are however two exceptions. First, USEtox is a human and environmental toxicity impact category, developed under the UNEP/SETAC Life Cycle Initiative. It is a consensus model amongst the major existing toxicity methods. The participating developers agreed on exposure routes and models to develop a ‘baseline’ toxicity model. Most importantly, the USEtox team developed an Excel based tool that allows practitioners to operate the model for their specific products and chemicals. They also developed a large dataset covering the most frequently occurring chemical (organic and metal) emissions. Whilst the USEtox team recognizes that there are still improvement areas, the deployment of such a calculation tool is instrumental to operationalize this impact category.

A second new impact category is water depletion. For many years, environmental impacts from water use were poorly handled in LCIA. Indicators such as eutrophication have a link to sustainable water management (related to excessive loading of some nutrients). As such some of the quality aspects of water release are partly dealt with in LCIAs. However, until recently, LCIAs were not modelling the potential environmental impacts from excessive use of freshwater. It is well known that with a growing global population we need to better manage the planet’s freshwater. A few years ago, scientists started to develop methods aiming to quantify the environmental impact from using freshwater.

A major difference in this modelling approach compared to previous impact categories is that impacts are highly complicated (water is important for all ecosystems) and effects are observed at a local level (due to a high spatial variation of water conditions). For this reason, developments are still in their early stages, with significant scientific improvements necessary. As with toxicity, it can be expected that LCA will require complementary tools to provide a comprehensive water evaluation.

With LCA being an important tool in sustainability assessments and sustainability aspects being included in many policies around the globe, it has become important to further standardize the approaches. This effort was undertaken in the International Reference Life Cycle Datasystem (ILCD) project, initiated by the Joint Research Centre of the EU Commission. A key deliverable is the development of a handbook. The project also commissioned a group of leading LCIA method developers to review existing LCIA methods. They evaluated existing methods in terms of scientific completeness, environmental relevance, scientific robustness and certainty, documentation, transparency, reproducibility, applicability and finally in terms of their stakeholder acceptance. Findings are in a report and recommendations are formulated for the use of life cycle based indicators in the context of sustainable production and consumption.