At the country level these principles are put into practice through a variety of means, including the following:

• Species and habitat conservation measures
• Environmental taxes and charges
• Negotiated voluntary agreements
• Deposit and refund, or take-back, schemes
• Restrictions on certain goods and practices

At the basis of most of these measures, and of the greatest relevance to the environment-trade interface, are environmental standards—particularly those imposed on traded goods. There are many types of environmental standards along the pathway of a product from extracting raw materials through manufacture, transport, trade, sale, use and disposal. They can be grouped under five headings.

Environmental quality standards seek to describe the state of the environment. Environmental standards can be concentrations of certain substances in the air, water or soil. They can be "critical loads," a level of deposition of pollutants below which some elements of the environment are not damaged. They can be population standards requiring the protection of certain species that have become threatened or endangered.

Emission standards identify the amount of certain substances a facility may emit. Emission standards can have a significant impact on production processes that are regulated, since it is generally better to avoid producing pollutants than to capture them at the end of the production process, creating a waste stream that must in turn be managed.

Product standards specify certain characteristics that are deemed necessary to avoid environmental harm from the use or disposal of products. For example, the use of lead in household paints has been banned because some of that toxic heavy metal is likely to reach the environment and pose a hazard, and chlorofluorocarbons have been banned from use in aerosols because they destroy the stratospheric ozone layer. Product standards are frequently used to protect human health.

Process and production standards specify how products are to be produced and what kinds of impact they may have on the environment. Standards based on process and production methods take on significance in international trade that they completely lack at the domestic level. Applied to traded goods, they amount to the regulating country setting standards on economic activities in the country of production.

Performance standards require certain actions, such as environmental assessment, which are expected to improve environmental management.

It is possible to combine all of these measurements and standards when analyzing the full impact of a single product—to consider all the environmental impacts of a product's production, use and disposal, and to combine them in a single life cycle analysis. An LCA can be used to identify opportunities to reduce environmental impacts, or to compare the environmental impacts of otherwise "like" products—for example, cloth diapers and disposable diapers, or different kinds of beverage containers. LCAs by definition look at a large number of categories of environmental impacts—for example, water and energy use, and release of various pollutants. The problem in comparing products lies in adding up the various types of impacts—and deciding how to weight them—to calculate an overall measure of environmental impact.

The overall effect of all these standards is to force producers, traders and consumers to consider the environmental impact of the economic decisions they take; in other words, they must begin to internalize the external environmental costs in their calculations. It is of course possible to achieve the same goal by using market-based instruments such as taxes, charges, tradable permits or subsidies. The advantage of such instruments is that they are generally more economically efficient. Their drawback is that, like standards, they require precisely articulated environmental goals as well as constant monitoring to ensure that the desired results are being achieved. It is important to recognize, however, that all of these measures, both regulatory and market-based, result in structural economic change as environmentally desirable activities are favoured and environmentally undesirable ones disadvantaged.

This large number and variety of standards, usually used in combination rather than alone, create an extensive management structure in which each standard complements the other, and few if any are effective just by themselves. They all have economic implications, creating potential problems for the trading system, which has thus far dealt mostly with product standards.

2.4.1 MEAs: Structure