Ecotoxicity and biodegradability of an alkyl ethoxysulphate surfactant in coastal waters

Abstract

Alkyl ethoxysulphates (AES) are anionic surfactants widely used in numerous commercial and industrial applications. In spite of the high AES volume consumption a few data concerning the occurrence, fate and effects of AES in marine environments are reported in literature. The objective of this study is to evaluate the biodegradability and toxicity of AES in pristine sea water. Ultimate biodegradation was studied according to the guideline 835.3160 “Biodegradability in sea water” proposed by the United States Environmental Protection Agency (USEPA). Acute toxicity of AES was studied to the microalgae Nannochloropsis gaditana, Isochrysis galbana, Chaetoceros gracilis, Dunaliella salina and Tetraselmis chuii and the invertebrate Artemia franciscana, using culture growth inhibition and death, respectively, as effect criteria. During the degradative process two different stages were observed, which were better described with the first order and logistic kinetic models, respectively. Lag times were 3.3 (stage A) and 26.5 (stage B) days whereas half-lives were 18.6 (stage A) and 49.8 (stage B) days. AES inhibited the microalgae growth, with 96-h EC 50 values ranging from 4.68 g L − 1 for D. salina to 24.02 mg L − 1 for I. galbana. Mean 48- and 72-h LC 50 values for A. franciscana were 38.30 and 23.92 mg L − 1 , respectively. The results indicate an extensive biodegradability of AES in sea water, although at a very slow rate. Acute toxicity was highly dependent on the species tested, being the green alga D. salina the most affected organism. The present study provides relevant data concerning the biodegradability and adverse effects of an AES surfactant on marine organisms, which are useful to establish water quality criteria in a regulatory framework.