Certification examples Sediment

Besides the preliminary stability study, regular checks should be carried out over the entire lifetime of the material. In some rare situations over the certification projects conducted under the BCR activities, examples of instability of substances in materials were demonstrated. A typical example was shown by the instability of TBT demonstrated in the CRM 462 (coastal sediment) at +40°C over a short-term period and at +4°C over 24 months which justified the withdrawal of the material from the market and its re-certification (Lamberty et at., 1998). 

The most obvious sources of error in analyses are related to insufficient extraction, low and irreproducible recoveries, insufficient peak resolution in chromatography, and the transformation of mercury species that may lead to artifacts. In the case of solubilized samples such as fish and mussels, speciation analysis was generally successful. However, with solids, techniques to remove or solubilize MeHg are complicated to validate by using spiking or tracer approaches, as it is difficult to prove that complete extrac-tion/separation has been achieved. A classical example of this difficulty is speciation of MeHg in sediments and soils. The only feasible approach adopted in certification of MeHg is to use different analytical approaches - that is, various extraction/sep-aration schemes and detection methods... 

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