Account for fact that background level now coded in Limit via use of same EMS code

ie 


Colour Apparent | Total | EMS_0001 | Aquatic Life - Freshwater | Water | Long-term chronic | 30 | 5 | mean |   |   |   |   | No Effect | Lower Limit | EMS_0001 * 0.8 | white light
-- | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- | --


