SMT4-CT97-2187 Labelling biodegradable products

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Biopolymers/Gums : Composts/Fertilisers : SMT (Standards, Measurements and Testing) Programme

Final Summary Report (118 Kb PDF)
Final Report (860 Kb PDF)
Final Report Annex and Appendix (993 Kb PDF)
Read Me file for Modelling Software (6 Kb PDF)
Modelling Software (178 Kb DOS Executable File)

Conclusions

Since the end of the 90s, the market of biodegradable materials has been booming, especially in the agricultural sector (horticulture). Both an increase of the biodegradable plastics available on the market, and an increase in the production capacity of the biodegradable products have been noted. Over the last years, not only the biodegradation properties of these products have been improved but also the prices have decreased, accelerating the demand for such products. Prices of biodegradable materials are now 3 or 4 times higher than the PE ones (it was 10 times at the end of the 80s, and prices similar to the PE are expected within 5 years). The major constituents of biodegradable products are polymers in particular, starch and various types of polyesters. There are currently more than 30 different biodegradable products on the marked. Beside the agricultural sector, biodegradable products are predominantly used for packaging, and in the hygiene sector.

However, the existing methods for the biodegradability measurement as well as for the assessment of the impact on the environment are not satisfactory because they are focused on composting tests and on packaging materials. It is therefore necessary to develop and to improve methods taking into account the influence of general environmental conditions on the degradation behaviour such as anaerobic conditions, degradation in soil, toxicity impact, etc. Furthermore, biodegradable products should be labelled to provide adequate information to the users and the consumers.

This is why this project has been launched and funded by the European Commission. The aim of the research project was threefold: (1) to assess the biodegradability of existing products (2) to develop and adapt suitable toxicity tests, and (3) to draft guidelines for the labelling of biodegradable products.

For the biodegradation assessment more than 10 methods have been tested on 20 selected materials. In general, in compost conditions the degradation is much more pronounced than in soil. The compost medium is more aggressive (high temperature, important hydrolysis) than the soil medium. Other discrepancies in the test results could also be attributed to the duration of the test. The time scale is therefore a key parameter that should be standardised in each method. There is not a direct relation between the degradation percentages obtained with laboratory tests and those obtained with samples placed in real situations. But the variations could be explained either by the human expert judgement or by the modelling which takes into account several external factors such as the climate of the site, the type of soil and the initial properties of the materials.

In addition to the biodegradation measurements, ecotoxic tests have to be carried out. Both tests are very linked. For the ecotoxicity assessment, several tests have been performed. The new test method with Vibrio fischeri bioluminescent bacteria, was suitable for compost toxicity measurements and very well correlated with the plant growth tests. The tested materials did not show any toxic effect with these tests. To elaborate a good toxicity test battery for compost applications, it requires more further information about the suitability of the existing methods and co-operation between standardisation organisations and researchers as well as policymakers.

In parallel with the toxicity tests, the impact of the biodegradable plastics on the industrial composting process has also been tested. The materials have been mixed at the rate of 1% with various green wastes in order to test the effect on the efficiency of a commercial waste disposal system. Adding 1% of materials has no negative effect of on the composting process, neither on the windrow aeration, nor on the biological reaction and on the quality assessment of the final obtained compost (agronomic value, visual aspect and phytotoxicity).

The tests to assess biodegradability are very long; up to 6 months for lab tests, and 2 years for in real soil tests. To reduce this duration, trials were carried out in order to propose accelerated laboratory tests. The parameter studied to accelerate these tests was the temperature. But this parameter was not set at the same level according to the nature of the used micro-organisms. Nevertheless, for the Sturm test an increasing of temperature up to 37°C should be recommended whatever micro-organisms source (in the best cases, the time reduction could be one or two weeks).

Another means to avoid these long duration experiments is to use biodegradation modelling and computer models. In addition, modelling allows to better understand the biodegradation phenomenon and to identify the key parameters. This is why biodegradation modelling has been investigated using statistical methods. Modelling aims at predict the in soil biodegradation rate versus the characteristics of the material and of the site where the material is buried. Modelling has established that the main parameters are the biodegradation rate measured with the Sturm test, the hydrophobicity content, the thickness, the N content and soil silt (slime) content. Based on this study, a computer model has been built and calculates the in soil half-life biodegradation duration of a given material for a given soil of burying. This model could be an excellent tool for the expert, or for the agricultural technician or for the manufacturer to predict the global behaviour of an existing material, or to design a new material.

As a synthesis of the above work, general and standardised guidelines for evaluating and labelling biodegradable products in relation to their biodegradability and environmental fate during use have been proposed. Considering the current trends in the use of biodegradable plastics, two guidelines have been developed, one for products that are designed to be composted, and one for products that are designed to disintegrate in soil during or after use in agricultural applications such as flowering pots and mulching films.

These guidelines recommend for instance to avoid any accumulation of plastic in the soil and to pay attention to the effects of plastic accumulation on the soil organisms (eco toxicity), the soil structure, the soil properties and the plants. Furthermore, the impact of the food chain should be considered (no toxic effect).

These guidelines and the present report will be distributed widely among the end users (industrials, consumers, and farmers) and the standardisation-labelling committees.