Using Environmental Simulations to Test the Release of Hazardous Substances from Polymer-Based Products: Are Realism and Pragmatism Mutually Exclusive Objectives?

Abstract

The potential release of hazardous substances from polymer-based products is currently in the focus of environmental policy. Environmental simulations are applied to expose such products to selected aging conditions and to investigate release processes. Commonly applied aging exposure types such as solar and UV radiation in combination with water contact, corrosive gases, and soil contact as well as expected general effects on polymers and additional ingredients of polymer-based products are described. The release of substances is based on mass-transfer processes to the material surfaces. Experimental approaches to investigate transport processes that are caused by water contact are presented. For tailoring the tests, relevant aging exposure types and release quantification methods must be combined appropriately. Several studies on the release of hazardous substances such as metals, polyaromatic hydrocarbons, flame retardants, antioxidants, and carbon nanotubes from polymers are summarized exemplarily. Differences between natural and artificial exposure tests are discussed and demonstrated for the release of flame retardants from several polymers and for biocides from paints. Requirements and limitations to apply results from short-term artificial environmental exposure tests to predict long-term environmental behavior of polymers are presented.

Keywords: artificial weathering; degradation; environmental simulations; leaching; polymer-based products; soil contact.

Figure 1

Possible consequence for chemicals under environmental relevant conditions in general.

Figure 2

Examples of concentration patterns in elute fractions from the dynamic surface leaching test that indicate different release mechanisms as described in [40]. On the x-axis, the period of water exchange in days is shown for (a) a process controlled by water solubility, (b) first flush (c) a diffusion-controlled process, and (d) first flush combined with a diffusion-controlled process.

Figure 3

(a) 24-h weathering cycle with continuous irradiation [70] and (b) weathering chamber prepared for exposing samples of synthetic athletic tracks.

Figure 4

Trend of (a) Zn content in solid matter in the course of the artificial weathering of three types of sports floorings (B1 to B3), as well as release of (b) Zn and (c) PAH measured in the eluates of intermittent batch leaching tests at L/S (liquid-to-solid ratio) of 2 L/kg during artificial weathering.

Figure 5

Release of Zn as a function of the liquid-to-solid ratio from high-density polyethylene (HDPE) granules in a column leaching experiment. The greatest release was observed in HDPE particles after 2000 h combined thermal and UV irradiation exposure. Converted to cumulative release, the displayed concentrations correspond to approx. 1% of the total Zn content [88].

Figure 6

Release of selected polybrominated flame retardants from PP (left) and PS (right) samples under different environmentally relevant conditions.

Figure 7

Application of different weathering scenarios: (a) soil bed test with flame-protected PP and PS samples and (b) real weathering experiments to evaluate the release of polybrominated flame retardants.

Figure 8

Cumulative emission curves for the biocides diuron, OIT (2-octyl-2H-isothiazol-3-one), and terbutryn from a vinyl acetate-based paint on wood. The amount of contact water is used to compare results from laboratory (EN 16105) and field experiments. During the laboratory experiment, each immersion cycle that consists of two immersion periods of 60 min represents 50 L/m² contact water (upper x-axis). Emissions during the field experiment are related to the collected runoff. The laboratory data represent mean values from four experiments, and the error bars indicate standard deviation. The laboratory data represent mean values from four experiments, and the error bars indicate standard deviation.

Figure 9

Comparison of experimental emission curves for the biocide diuron and emission curves obtained from a regression model that considers the various actual weather conditions. Boards painted with a vinyl acetate-based paint were exposed to natural weathering at two different sites in Berlin and 60 km north of Berlin and during different periods—resulting in six independent experiments. Runoff was collected after all rain events and analyzed for diuron. Area-related diuron emissions were calculated and demonstrated as cumulative emission curves.

Figure 10

Flow chart for the design of artificial environmental exposure tests. Top: required previous knowledge; center: options of exposure tests; bottom: expected results.