What is the “Top Two” approach?
In deriving generic or site-specific assessment criteria for soils, SR3 (Environment Agency, 2009) generally recommends using default inputs intended to be protective in all but the most extreme exposure scenarios. For example, with respect to the consumption of six groups of homegrown fruit and vegetables considered by the UK Contaminated Land Exposure Assessment (CLEA) model, it recommends that consumption rates that would be protective of 90% of the UK population (i.e. 90th percentile consumption rates) should be adopted.
In 2014, alternative guidance was published as part of the SP1010 research project (Defra, 2014), which also derived the initial six ‘Category 4 Screening Level’ (C4SLs). SP1010 generally recommends the use of “central tendency” inputs to avoid generating overly cautious assessment criteria. However, in order to ensure that assessment criteria are adequately protective, SP1010 recommends a “middle ground approach” with respect to consumption rates where by the 90th percentile is used “for the two homegrown produce groups expected to give the highest exposure” and mean consumption rates for the remaining four groups. This is known as the ‘Top Two’ approach.
CLEA V 1.071
There is functionality within the latest version of CLEA (Ver. 1.071) to implement the recommendations of SP1010, and so generate C4SL-like assessment criteria. However, in order to apply the ‘Top Two’ approach the user must first be able to identify and definethe ‘Top Two’ produce groups within the chemical-specific database. Therefore, in order to produce C4SLs (or any other SP1010-compliant assessment criteria) a risk assessor must first identify which are the ‘Top Two’ produce groups. This is not straightforward or readily decided and requires a series of calculations.
But how can the ‘Top Two’ be identified?
LQM have developed a ‘Top Two’ Calculator, which rapidly and easily identifies the Top Two, and we have been using internally for sometime. To find out more about the ‘Top Two’ approach, and how to use the Calcuator to identify the ‘Top Two’ produce groups please join us for a one-hour lunchtime webinar on the 5th of Sept 2018. To book your place please visit our website.
** Each delegate will also receive a free complimentary copy of the LQM ‘Top Two’ Calculator. **
Note: webinars can only be booked via online card payment but you will receive a 20% discount making the overall cost £50 excl. VAT.