His work has focused on the evaluation of environmental health risks in special populations, such as children, farm workers, and farm producers. Specialty areas include health risks of pesticide exposures, development of new exposure assessment methods. He established the use of fluorescent tracers to evaluate worker exposure and protective clothing performance, and introduced urinary metabolite monitoring as method for assessing children's exposure to pesticides. He received the 2006 NIOSH Director’s Award for Excellence in Research and the 2007 Jerome Wesolowski Award for Outstanding Contributions to the Field of Exposure Science from the International Society of Exposure Science. Dr. Fenske served as a member of National Academy of Medicine Roundtable on Environmental Health Sciences, Research, and Medicine for 12 years. In 2008-2009 Dr. Fenske was Chair of the National Academy of Sciences Committee to Review the Health Effects of Vietnam Veterans of Exposure to Herbicides (Seventh Biennial Update), and served from 2006-2009 as a member of the Environmental Protection Agency's Human Studies Review Board. He also authored the Chemical Hazards section of the International Labor Organization’s Protocol on Agricultural Health and Safety in 2009. He continues in his efforts to minimize the health risks of pesticides.