Environmental Emission of Wood Preservatives: Interpretation of Data Relevant to BPD Risk Assessments

IRG/WP 09-50259

D G Cantrell

The risk assessments for the use of wood preservatives proposed by the OECD and used under the Biocidal Products Directive (BPD) (98/8/EC) require the derivation of leaching rates for active substances. These rates are to be used as input data in to agreed exposure scenarios. The leaching rates can be derived from laboratory testing and from field testing. The relationship between laboratory and field tests has been studied in order to determine the correlation between the two modes of testing. EN84 tests have been used as a method. However, the determination of environmental leaching rates is beyond the scope of this test and it has been found to over-estimate leaching. The OECD guideline 1 (dipping) test has been designed specifically to determine environmental leaching rates from UC3 wood. This paper compares the leaching fluxes derived from OECD guideline 1 dipping tests to those derived from field tests. This allows a comparison of both the magnitude of flux rates and leaching flux profiles derived from the two tests. The magnitudes of the flux rates require the application of correlation factors in order to get agreement; these factors are presented and found to be of the order 5 – 10. The leaching flux profiles are found to be very different when the flux rates are plotted against time. The laboratory test gives an “exponential” profile, i.e. a profile that decreases quite sharply with time and then levels off. The field test produces profiles that are “sawtooth” patterns with time. This “sawtooth” pattern correlates with rainfall. This is in agreement with, and confirms, data previously presented (Baines, 2008). In the present study, however, an alternative method of data analysis is explored. If the field data is normalised according to the amount of rain falling then it is found that the laboratory and field tests produce very similar leaching profiles. Thus, the contrast previously discussed is shown to be an artefact of the method of analysing the data obtained from field tests. This is due to the inherent variability of weather patterns with time that cannot be replicated in the laboratory. If annual average rainfall figures are used, the risk assessments at differing time points can be carried out as assessments at average rainfall amounts. This alternative method of data analysis according to rainfall rather than time suggests a method of analysing the models for OECD risk assessment that can increase their utility.


Keywords: BPD, risk assessment, UC3, laboratory test, field test, analysis

Conference: 09-05-24/28 Beijing, China


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