¹ Faculty of Agrotechnology and Food Science, University Malaysia Terengganu, 21030 Kuala Terengganu, Terengganu, Malaysia
²Faculty of Maritime Studies and Marine Science, University Malaysia Terengganu, 21030 Kuala Terengganu, Terengganu, Malaysia

*Corresponding author: hii@umt.edu.my

Abstract

   The effects of two widely used pesticides in paddy fields, 2, 4-D, dimethylamine and endosulfan on growth, photosynthetic rate and the photosynthetic pigments of Chaetoceros sp. and Nannochloropsis sp. were assessed in this study. The forty-eight hour 50% inhibitory concentration (IC₅₀) values for 2, 4-D dimethylamine on Chaetoceros sp. and Nannochloropsis sp. were 142.2 mg l^-1 and 211.8 mg l^-1, respectively, and the 48 hour IC₅₀ values for endosulfan on Chaetoceros sp. and Nannochloropsis sp. were 21.9 µg l^-1 and 45.8 µg l^-1, respectively. Thus, endosulfan was much more toxic to the microalgae than 2, 4-D dimethylamine. Both pesticides reduced photosynthetic pigments and oxygen production rate. After 48 hours exposure to the pesticides, the microalgae were transferred to a pesticide-free medium to investigate the post-exposure effect. Results revealed that 2, 4-D dimethylamine and endosulfan did not cause irreversible damage on the microalgae. However, there was a prolonged lag phase and the maximum specific growth rate (µ) of the microalgae was significantly retarded.