University of Iowa researchers have identified a chemical that may dampen mating interest and affect male reproduction in aquatic species.

The researchers in the Department of Biology tested the effects of dimethyl phthalate, a chemical used by some industries and found in consumer products such as insect repellent and plastics. The test subject was a freshwater snail native to New Zealand that has spread worldwide and is considered a bellwether for how other aquatic organisms may be affected by pollutants.

The male snails were divided into two groups and given either a low or high concentration of dimethyl phthalate for five weeks. The biologists found that the group that received the highest chemical concentration was 69% less likely to attempt to mate with female snails than a group of male snails not given any chemical. Moreover, the researchers observed that sperm from the chemical-exposed males was physically altered, which could affect reproductive success.

The findings build upon previous research that found sperm-altering or metabolism-linked effects to rats, mice, and mussels from phthalates, a class of chemicals used in plastics manufacturing that includes dimethyl phthalate. A separate study in 2002 found a link between humans exposed to phthalates and decreased testosterone levels. This study expands those findings by showing chemical effects on mating behavior in one species.

“Our study outcomes are both exciting and disturbing in indicating that exposure to a chemical that frequently leaches into water from commonly used plastics can alter sperm and mating behavior in a snail used as a ‘canary in the coal mine’ indicator for water quality,” says Maurine Neiman, professor in the Department of Biology and a study co-author. “This link between plastics and important reproductive traits should bolster the case to reduce plastic use and waste for the sake of preserving human health and aquatic ecosystems.” 

The study’s corresponding author is Bryan Guevara, who graduated from Iowa in 2023 with a degree in biology and is currently a graduate student at Indiana University-Bloomington.

Co-authors include Nadia Patel and Yi Tu. They were high school students who joined Neiman’s lab as part of the Secondary Student Training Program run by UI’s Belin-Blank Center. Patel is a senior at Cedar Falls High School who will attend Brown University this fall. Tu was at The Bishop School in San Diego and is now a freshman at Rice University.

“Leading this study as an undergraduate was an incredible opportunity to contribute to meaningful scientific research,” Guevara says. “I also had the opportunity to mentor high school students. Seeing their curiosity and growth in the lab made this experience all the more rewarding." 

The study, “Phthalate exposure influences mating behavior and sperm morphology in an aquatic ecotoxicology model system,” was published online Feb. 26 in the journal Aquatic Conservation: Marine and Freshwater Ecosystems.

The U.S. National Science Foundation, the Belin-Blank Center and the Iowa Sciences Academy at the University of Iowa, and Linda and Rick Maxson funded the research.