Stories in the Sediment: DDD Use at Expo 67

Abstract

The toxic, persistent pesticide dichlorodiphenyldichloroethane (DDD) was used liberally prior to and during the World Exposition of 1967 (Expo 67) on Île Sainte-Hélène in Montréal to reduce the population of nuisance Trichoptera insects (also called caddisflies or shadflies) in the area. Sixteen thousand kilograms were applied over six periods in two years. Despite reports by the project leaders that the practice was not detrimental to the ecosystem and that DDD was not detected downstream in significant concentrations following applications to the river, further investigation was required to determine the occurrence of the pesticide, and its concentrations. Given the large volume of pesticide that was applied to the river, I hypothesized that there would be a strong DDD signal in sediments downstream of the Expo 67 site. I obtained a sediment core from the bay of Île de Grâce at the mouth of Lac St Pierre in the St. Lawrence River, downstream of Montréal. The core was sliced, dated radioisometrically, and analysed for the presence of dichlorodiphenyltrichloroethane (DDT) and related pesticides using gas chromatography. The isotopes cesium-137 (137Cs), radium-226 (226Ra), and lead-210 (210Pb) were used to establish dates of sediment deposition. Loss on ignition was used to determine organic carbon content. Stable lead content was analysed because it may also support sediment ages. Concentrations of DDT, DDD, and dichlorodiphenylethylene (DDE) ranged from below the detection limit to 3.3 parts per billion (ppb), 57.7 ppb, and 17.1 ppb, respectively. Adjusting the concentrations to reflect organic carbon content did not significantly affect the trend in concentration by depth. Peaks in DDD concentrations and related compounds were discovered that correspond to the Expo 67 applications. These findings demonstrate that DDD was present in unusually high concentrations (well above the probable effect level of 8.51 ppb (Ontario Ministry of the Environment)) in the St. Lawrence River in 1967, potentially exposing a wide variety of organisms. This finding may also be used to inform future decisions regarding the management of the St. Lawrence Seaway. I also investigated the role of fragmentation, specialisation, and interdisciplinarity in this research, and critically examined the historical context of this project in order to pursue knowledge of this field with as full an understanding of it as possible.