Triazine and Metolachlor Herbicide Residues in Farm Areas of the Lower Fraser Valley, British Columbia, Canada

Crop soils, ditch sediments and water flowing from several Lower Fraser River (LFR) farm areas of British Columbia, Canada, to salmon tributary streams of that river were sampled in 2004–2005 to quantify for residues of triazine [atrazine, desethylatrazine (a transformation product of atrazine), propazine, and simazine] and metolachlor (a chloroacetamide) herbicides. Average concentrations [μg kg⁻¹ dry weight (d.w.)] of triazine (10,110) and metolachlor (8,910) herbicides detected in crop soils at the start (May 2004, 2005) of the growing season were about 17 and 6 times, respectively, higher than those found for both herbicide groups during (June–Sept, 2004, 2005) the growing season. In contrast, mean concentrations (μg L⁻¹) of triazines (0.092) and metolachlor (0.014) in permanent ditches adjacent to farms were about 7 and 28 times, respectively, lower at the start than during the growing season. Both herbicide groups in ditch sediments were detected only during the growing season at concentrations averaging about 315 μg kg⁻¹ d.w. The risk potential of these herbicides for non-target aquatic organisms inhabiting permanent farm ditches contiguous to tributary streams of the LFR during the growing season is evaluated and discussed.

Key Words:

• Atrazine
• Triazine herbicides
• Metolachlor herbicide
• Lower Fraser River

ACKNOWLEDGEMENTS

Funding for this study was provided by Environment Canada, Pacific & Yukon Region, Vancouver, BC, under the 5-year Georgia Basin Action Plan. The technical staff, notably L. Chow and J. Mazur, of the PESC Organic Chemistry Laboratory, North Vancouver, B.C., Canada, are gratefully acknowledged for the analyses of environmental samples. We are also grateful to L. Suffredine for her assistance in field sampling, and the farmers of the study sites for their co-operation and the use of their farms for sampling and other observations.

Notes

^†IUPAC = International Union of Pure and Applied Chemistry.

^†Ions used for quantification (1st ion) and identification (2nd and 3rd ions) in selected ion monitoring (SIM).

^‡ Mean% (range) of (a) Field blanks (n = 2) (top line); (b) Laboratory QC (n = 7) (mid-line); (c) ‘Blind’ QC (n = 6) (italicized third line), spiked at 5 & 10 times MDL to 4.5 L water (only 0.8 L extracted) and to 400 g sediments (10 g extracted) of matrices from Control areas; [sediments/soils moisture content = 49% ± 3 (19–76%); n = 8].

^†Figure 1: loamy sand soils (1, 3, 4–9, 11); muck soils (2, 12, 14, 17, 18); silt loam soils (10, 11, 13, 15, 16).

^‡Soil moisture = 26% ± 2% (17–45%; n = 20); sediment moisture = 45% ± 3% (19%–75%; n = 15).

^§2005 isolated, temporary farm pools (<5.0 m², 0.10 m depth; n = 5).

^¶Start of growing season soil treatment (<a week) in May 2004, 2005; sampling program began after two major rainfall events in June–September 2004, 2005.

^#Shown are mean of positive findings, range, and frequency (n/x, where n = number of samples above detection limit, x = number of samples).

^††ND = not detected; detection limits: soils and sediments = 10–20 μg kg⁻¹, water = 0.005 μg L⁻¹.

^†EEC_max = maximum estimated environmental concentrations in permanent farm ditches (D) and isolated, temporary farm pools (P) (<5 m²; 0.1 m depth, n = 5).

^‡CWQG = Canadian Water Quality Guidelines.²³

^§RQ = EEC_max ÷ guideline concentration; increasing multiples = increasing risk potential for non-target aquatic organisms.

^¶Not designated by CWQG; the number assigned to atrazine is used.

^#NA = not available.