Metals compostability standards

Acid-digestion is often used with composts derived from municipal wastes, sewage and slurry, where toxic amounts of heavy metals may cause problems on the land to which they are applied. It is probably more convenient to determine total elements in soils by a benchtop X-ray fluorescence spectroscopy (XRF) instrument. This only requires the soil to be ground, and several reference standards of a similar soil. A Reference Materials Catalogue, Issue 5, 1999, is available from LGCs Office of Reference Materials, Queens Road, Teddington, Middlesex TW11 OLY, UK. Tel. -i-44 (0)20 8943 7565 Fax h-44 (0)20 8943 7554. 

ASTM D6400. In 1999 ASTM announced its Standard Specification for Compostable Plastics (D6400-99). The standard establishes criteria to be met before a product can be labeled compostable. Briefly a product must, at minimum, satisfy ASTM tests showing conversion to carbon dioxide at 60% for a homopolymer or a statistical random copolymer and 90% for other types of copolymers and blends in 180 days or less, and leave no more than 10% of the original weight on a 2-mm screen. If carbon-14 tests are used a test period of 365 days is allowable. Environmental toxicity issues are also addressed, including limits for heavy metals. The ASTM standard has coimterparts in German (DIN 54900), European (EN 13432), and international (ISO 14855) documents. 

Compost quality guidelines are relatively new, dating to the mid-1980s [24]. There has been a steady progression of definitions of contaminant limits when considering compost quality. The very first published limits pertained to heavy metals and were seen in the late 1970s in Europe. These standards include ... 

EN 13432 No toxic or harmful substances Minimum 50% organic material Heavy metals limits relative to compost quality criteria European national standards for chemical composition Ecotoxicity tests with two plant species... 

The testing procedure is slightly different the Controlled Composting Test . DIN 54900 (in press) defines Biodegradable polymers and measures the ecotoxicity and heavy metal content. The method will be very similar to the CEN standard. 

Potential hazards caused by the introduction of toxic components (especially heavy metals) with contaminated compost are revealed very often. These typical impurities are covered by the analytical quality control of most of the national regulations in Europe and will lead to a classification as second or third quality and to a limited use of the compost. These national standards are dealing with well-known contaminants that may derive from typical biowaste and are focussing on heavy metals and a handful of halogenated or aromatic hydrocarbons. The inclusion of bioassays with higher plants in some standards is more to determine the maturity of the compost than with the appearance of ecotoxic effects caused by anything other than the chemicals being determined. 

At the start in 1997 the system was based on the DIN V 54900 [4] prenorm on compostability of plastics. In addition to the norm a certification scheme was published in which some further (technical) rules for certification were specified. These can considered to be a kind of by-law. At the third revision of this certification scheme published in July 2001 [14], the EN13432 [5] and ASTM D6400-99 [54] norms are also mentioned besides the DIN V 54900 as standards along which the compostability can be evaluated. On a few matters of conflict, e.g., heavy metals and test duration of radiolabelled biodegradation tests, the scheme is giving the ultimate guideline for the certification to follow. 

The highly instrumented tunnels in the composting plant hold 90 m of waste. In the trials of our material the input to one of the tunnels contained just over 1 wt% of LDPE bags (10,000 bags), which contained the TDPA additive but were not pre-aged. The compost was examined after the main maturation period (2 weeks in the tunnel), after post-maturation (12 weeks outdoors) and after six months, all according to Austrian National Standard ON S 2200. Test protocols included mass loss, analysis for heavy metals and tests of seed germination and survival of daphnia and earthworms. 

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