Science Serving Maryland's Coasts

Sara Gottlieb, College of William and Mary

Class Year: 

Project Title: 

Effect of the Herbicide Alachlor on Aquatic Microorganisms of the Patuxent River


The impact on microoganisms (<1.6 microns) of alachlor in varying concentrations was investigated during the summer in closed system batch incubations.  Micrroorganisms in water filtered from the Patuxent River at the Chesapeake Biological Laboratory were exposed to alachlor at concentrations ranging from 0.002 to 20.0 mg/L along with controls in replicate BOD bottles and incubated for five days during each of three experiments.  Microorganism concentrations and dissolved oxygen remaining were measured at the end of the incubations.  Gas chromatograph analysis was performed to determine the final concentration of alachlor in one of the samples.  Alachlor had a significant effect on both factors at the 20.0 mg/L concentration in the second experiment and at the 2.0 mg/L concentration in the third one, however each effect was the opposite of that in the second experiment.  A negative relationship between microorganism concentration and total community respiration was noted in two experiments. The explanation for the observed results is elusive due to possibly varying effects on genera of microorganisms within the examined assemblages.  An almost total loss of initial the initial amount alachlor was noted in the sample quantified at the end of the incubations.