Toxicologie environnementale et analytique

Deposition and Distribution Factors for the Endocrine Disruptor, 4-Nonylphenol, in the Sierra Nevada Mountains, California, USA

Abstract

Rebecca A Lyons and Lisa Benvenuti

4-nonylphenol (4NP), a breakdown product of nonylphenol polyethoxylate, is a potent endocrine disruptor and persistent organic pollutant (POP). Due to physical and chemical properties, 4NP is capable of long range transport as both an aerosol and attached to dust particulates. Since nonylphenol polyethoxylates make up a substantial portion of many pesticides, agricultural regions are often sources of 4NP. Physical barriers such as mountain ranges may alter the distribution of this POP but does not stop the long range transport. The Central Valley of California, USA is an intensely farmed region adjacent to the Sierra Nevada Mountains subjected to onshore prevailing winds from the Pacific Ocean. Previous work revealed that the winter snow pack in the Sierra Nevada showed at least an order of magnitude more 4NP than surface water during summer months. As a result, spring melt water may send high concentrations of 4NP to organisms during critical developmental periods. Physical and geographical characteristics of snow and terrain were assessed to determine which factors affect 4NP accumulation in snow and regions at higher risk of 4NP exposure. Samples were taken from snow, surface water and atmospheric deposition for four consecutive years and analyzed by gas chromatography-mass spectroscopy for 4NP. Snow water and dust particulates in snow were analyzed separately. Additionally, snow chamber simulations were run to assess snow characteristics that would lead to increased 4NP deposition in snow. Wind speed was found to correlate inversely with 4NP deposition. Snowflake size showed a positive correlation with 4NP deposition due to increasing surface area. The amount of dust in snow was poorly correlated with 4NP concentration. A geospatial model was developed for the Eastern Sierra Nevada using ArcGIS software that included wind speed, snowflake size, and topographic shielding. Regions that were predicted to be at high risk for 4NP deposition correlated strongly with empirical data from the field.