Chemical characterisation of a new estuarine pollutant (2,4-Dichloro-6-Nitrophenol) and assessment of the acute toxicity of its quinoid form for Artemia salina

It is known that the compound 2,4-dichloro-6-nitrophenol (2,4DC6NP) is formed upon nitration of 2,4-dichlorophenol, which in turn is a transformation intermediate of the herbicide dichlorprop. However, the chemical and spectroscopic characteristics of 2,4DC6NP, as well as its toxicity, are poorly known. This work shows that 2,4DC6NP behaves as a diprotic acid in aqueous solutions, with pK(a) values of 3.0 +/- 0.9 and 4.9 +/- 0.5. At pH < 3, 2,4DC6NP would undergo protonation. The absorption spectra suggest that anionic 2,4DC6NP, which prevails at pH > 5 would have an ortho-quinoid structure that is responsible for the absorption peak centred at 428 nm. Considering that 2,4DC6NP has been detected in the brackish lagoons of the Rhone delta (southern France), where its levels are comparable to those of the parent herbicide, it is necessary to examine the possible effects of 2,4DC6NP on the species living in that environment. For this reason, the acute toxicity of the anionic form of 2,4DC6NP was assessed for the brine shrimp Artemia salina, a zooplankton species that lives both in brackish and in saline aquatic environments. The toxicity test yielded a LC20 value of 8 +/- 2 mg L-1 and a LC50 value of 18.7 +/- 0.8 mg L-1. Such values are safely higher than the maximum detected concentration of 2,4DC6NP in the Rhone delta lagoons. Further studies should be concentrated on the long-term effects of 2,4DC6NP, and in particular on its potential genotoxicity.