Comparing Herbicide Behaviour and Exports in Contrasting Toronto Watersheds

Session: 58. - Cities on the Shore: Urbanization as a Growing Threat to Nearshore Ecosystem Health

Abha Parajulee, University of Toronto Scarborough, [email protected]
Ying Duan Lei, University of Toronto Scarborough, [email protected]
Xiaoshu Cao, University of Toronto Scarborough, [email protected]
David McLagan, University of Toronto Scarborough, [email protected]
Leo Yeung, University of Toronto, [email protected]
Carl Mitchell, University of Toronto Scarborough, [email protected]
Frank Wania, University of Toronto Scarborough, [email protected]

Abstract

We investigated late fall and winter dynamics of four herbicides in paired urban and rural watersheds in Toronto, Canada during rainfall and snowmelt, six to seven years following a ban on their cosmetic use. The range of average concentrations and loads of the sum of atrazine, metolachlor, 2,4-D and mecoprop overlapped in the two types of watersheds, with slightly higher average concentrations in the rural watershed. Relatively consistent herbicide concentration-discharge patterns (i.e. dilution) were observed in the urban sub-watersheds during rainfall, while concentration-discharge patterns were much more variable in the rural watershed. This suggests relatively uniform transport pathways across the urban sub-watersheds, compared to the rural watershed. Concentration-discharge patterns of the neutral herbicides atrazine and metolachlor were similar in both watersheds during snowmelt, though varying discharge patterns resulted in divergent timings of peak concentrations. In contrast, the acidic pesticides 2,4-D and mecoprop, which are primarily associated with urban uses, showed much more variable behavior across both watersheds and merit further investigation. Overall, this work highlights the need to consider pesticide dynamics throughout the year in order to more thoroughly assess the long-term efficacy of legislation governing their use.

1. Keyword
urban watersheds

3. Keyword
pesticides

4. Additional Keyword
agricultural watersheds

5. Additional Keyword
rainfall

6. Additional Keyword
snowmelt