Research Document - 2014/103

Estimates of the effects of sea lice chemical therapeutants on non-target organisms associated with releases of therapeutants from tarped net-pens and well-boat bath treatments: a discussion

By F. H. Page and L. Burridge

Abstract

This paper represents an initial and preliminary effort to combine the transport and dispersal results of Page et al. (2014) with the toxicity results of Burridge (2013) in an effort to give a more field-oriented perspective on the spatial and temporal scales upon which therapeutant toxicity potentials may occur. The approach taken is to use a hazard quotient approach, i.e., the ratio of the estimated in situ exposure concentration to the level of effect concentration. The estimates of in situ therapeutant concentrations are estimated from the transport and dispersal relationships for tarp and well-boat bath treatments given in Page et al. (2014) and the organism-specific levels of effect concentrations are given by the LC50 (the concentration at which 50% of test organisms die) and NOEC (the approximate concentration at which no lethal effect is observed) values reported in Burridge (2013). The results indicate that the horizontal spatial and temporal scales for potential toxic effects vary with the therapeutant, with the spatial and temporal scales increasing with the degree of therapeutant toxicity. The smallest scales (<100s of metres and minutes) are associated with Paramove®50 (active ingredient (a.i.) hydrogen peroxide) and the largest scales (kilometres and hours) are associated with Alphamax® (a.i. deltamethrin). The scales (100s of metres to a kilometre and minutes to hours associated with Salmosan® (a.i. azamethiphos) are intermediate to the other two therapeutants. It is also recognized that in order for these potentials to be realised, the in situ distributions of non-target organisms need to be such that they experience the above exposures.

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