Physiological and Biochemical Responses of Fresh Water Algae, Ankistrodesmus acicularis and Anabaena flos-aquae, to Dichlobenil Exposure

The herbicide dichlobenil is widely used to control unwanted weeds in non-agricultural areas and
aquatic environment. When released into environment, it may harm the growth of algae, which in turn
might disturb the balance of aquatic ecosystem. Herein, the physiological as well as the biochemical
responses of two fresh water algae, namely Ankistrodesmus acicularis (Chlorophyta) and Anabaena
flos-aquae (Cyanobacteria), to different concentrations of dichlobenil were assessed. Parameters,
including chlorophyll (a) Content, EC50 values, carbohydrate and adenosine triphosphate (ATP)
contents as well as the uptake by both algal species were evaluated. We found a significant decrease
in chlorophyll (a) content of both algal species to intermediate and high concentration of dichlobenil,
whereas stimulative effect was observed for low concentration of dichlobenil on Chl (a) content.
Attainable results derived by probit analysis revealed that the EC50 values at 5th and 7th days were
approximate to each other for both algal species. Furthermore, a drastic decrease (98%) in ATP
content was noticed at 8.0 mg/L dichlobenil treatment in case of Ankistrodesmus acicularis. On the
other hand, the activity of Anabaena flos-aquae cells was enhanced by the application of low and
intermediate concentrations of dichlobenil (0.25-4.0 mg/L). Notably, higher concentration level (16.0
mg/L) causes substantial decreases in ATP content. Ankistrodesmus acicularis was found to be more
sensitive than Anabaena flos-aquae. The uptake of dichlobenil was best fit to a pseudo-first order rate
kinetic. The specific uptake rate constants of dichlobenil in case of Ankistrodesmus acicularis were
considerably lower than the corresponding rates exhibited by Anabaena flos-aquae. The half- life
time for a given concentrations of dichlobenil was at variance for both algal species. Such variation in
the uptake rates and half- life time of dichlobenil for both algal species could have some implications
on the aquatic ecosystem.