Regulated Heavy Metal Testing

The degraded materials should not leave any regulated heavy metals in the compost soil after degradation. The compost soil from each of the degraded samples was tested for lead and cadmium for all of the materials. The acceptable limit is 30 mg/kg for lead and 0.3 mg/kg for cadmium. The compost soil for each sample was put into solution and the regulated heavy metal in the compost soil was measured with Fisher-brand (2013) hollow-cathode single-element 2-inch-diameter lamps with elements for lead and cadmium. 

Lead and cadmium were measured by flame atomic absorption spectrometry using a Jarrell-Ash Model. Lead and cadmium absorption was measured at 283.3 nm and 228.8 nm, respectively. The background correction was measured at 281.2 nm for lead and at 226.5 nm for cadmium. The detection limits are 0.02 ppm lead and 0.005 ppm cadmium in the analytical solution. For a 1-gram sample, the detection limits are 0.2 ppm Pb and 0.05 ppm Cd. 

The standard solutions and eight sample solutions were analyzed using a ThermoElectron S Series Flame Atomic Absorption Spectrophotometer and an air-acetylene flame and equipped with a Pb hollow-cathode lamp detecting at 283.3 nm, a Co hollow-cathode lamp, and a Cd hollow-cathode lamp. The sample solutions gave absorbance at or very near the lowest standard employed, which was just above the detection limit of the instrument. Using 0.022 ppm Pb as the detection limit leads to an upper limit of 20 ppm Pb + in the original soil samples. The 20-ppm value equates to 0.02 mg/kg for Pb. The Cd concentrations were lower than 1 ppm, which equates to 0.001 mg/kg Cd. 

All of the soil samples from the compostable materials had lead concentrations much lower than the limit of 30 mg/kg Pb and Cd concentrations lower than the limit of 17 mg/kg Cd. In fact, the measured values for Pb and Cd were at the lower detection limits of the Pb and Cd detectors. 

Fisherbrand (2013) Fisherbrand HoUow Cathode Single-Elemeiit 2 in. dia. Lamps with Elements Aluminum to Platinum, n.d., bttp //www.fisbersci.com (last accessed June 2014). 

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Regulated heavy metal testing measures the concentrations of regulated metals in the compost soil at the end of the biodegradation testing. 

Regulated heavy metal testing measures the concentrations of regulated metals in the compost soil at the end of the biodegradation testing. The compost samples must have regulated metal concentrations less than prescribed levels, listed in Table 8.3. 

The plastic sample also must pass several marine toxicity tests, including P0I540X (microbial oxygen absorption), Microtox (microbial bioluminescence) test, fish Acute Toxicity (static conditions) OPPTS 850.1075, Daphnia Acute Toxicity (static conditions) OPPTS 850.1010, or Static Algal Toxicity Test OPPTS 850.5400. The plastic samples must also have less than 25% of maximum allowable concentrations of regulated heavy metals. 

The fourth test procedure for ASTM D-7081-05 standard specifies that the plastic sample shall have less than 25% of the regulated heavy metal concentrations that is specified in the country where the product is sold. 

Safety considerations where the resultant compost should have no impact on plants, using the Organisation for Economic Co-operation and Development Guide 208, Terrestrial Plants Growth Test. Furthermore, the regulated (heavy) metals content in the polymer material should be 50% or lower than prescribed thresholds in the country of use (e.g., 50% in the US and in the Canadian Environmental Protection Agency s prescribed threshold). 

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