Pesticide Residues in Wash Off from Residential Hardscapes

Darren Haver*, UC Cooperative Extension Orange Tamara Majcherek, UC Davis, Plant Sciences Jay Gan and Sveta Bondarenko, UC Riverside, Environmental Sciences

Introduction • Residential Pesticide

Applications – Perimeter sprays around

buildings

– Spot treatments

– Applications directly on plant material

– Crack and crevice

Introduction continued -

• Hardscape surfaces – Driveways, walkways, and patios

connected

• Downspouts and Drains – Delivers storm water away from

foundation

– Landscape drainage pipes carries water to gutter

• Causes of Pesticide Movement – Rain

– Irrigation

– Car washing

– Cleaning hardscape

Introduction continued -

Introduction continued -

• Hardscape Wash Off – Approx. 5 gals/min of water

to wash driveways and sidewalks

– Higher pressure stream of water compared to irrigation

– May mobilize more debris (leaves, sediment, dust, etc…)

Questions

• Will washing off a hardscape result in a significant source of pesticides reaching the gutter?

• How long after the application of a pesticide can it be detected in wash water?

• Do landscapes designed to minimize runoff reduce pesticide loading to storm drains?

UC ANR South Coast Research and Extension Center

Experimental Site in Irvine, CA

Landscape A Typical Hardscape

Landscape A Typical Hardscape

Landscape B Low Impact Design I Hardscape

Landscape B Low Impact Design I Hardscape

Landscape C Low Impact Design II Hardscape

Landscape C Low Impact Design II Hardscape

Methods • Pre-Treatment Wash

– Background levels of pesticides (previous studies)

• Perimeter Pesticide Treatment

– 1 foot out, 1 foot up fan spray around perimeter using fipronil at a rate of .06% (0.96 g fipronil applied to each landscape).

• Lawn and Garden Treatment

– RTU hose-end product (0.3% bifenthrin or ≈ 0.94 g bifenthrin applied to each landscape)

• Hardscapes washed off at defined intervals following pesticide application.

Volume of Water Used at Each Wash off Event

Landscape Day 7 – Week 1 Day 14 – Week 2 Day 21 – Week 3 Day 28 – Week 4 Day 56 – Week 8

A 28 gallons 38 gallons 35 gallons 30 gallons 32 gallons

B 30 gallons 38 gallons 38 gallons 30 gallons 32 gallons

C 40 gallons 42 gallons 40 gallons 38 gallons 32 gallons

Pre-Treatment Baseline Pesticide Concentrations in Runoff

Bifenthrin in Wash Water

Bifenthrin in Wash Water

Bifenthrin Loading from Hardscape Washing

0.0

20000.0

40000.0

60000.0

80000.0

100000.0

120000.0

140000.0

TypicalLID I

LID II

1253

67.0

3292

7.0

2785

6.2

Nan

ogra

ms

of b

ifent

hrin

56 d

28 d

21 d

14 d

7 d

24 h

(13.8%) (4%) (3.4%)

Fipronil in Wash Water

Fipronil in Wash Water

Fipronil Loading from Hardscape Washing

0.0

2000.0

4000.0

6000.0

8000.0

10000.0

12000.0

14000.0

TypicalLID I

LID II

1290

5.0

1273

.0

476.

0

Nan

ogra

ms

of fi

pron

il

56 d

28 d

21 d

14 d

7 d

24 h

(1.6%) (.3%) (.19%)

Fipronil Breakdown Products

• Fipronil sulfide was not detected in any samples.

• Fipronil desulfinyl was not detected in the 24 h samples

– Low concentrations were detected in wash off from all three landscapes (7 day to 56 d)

• Fipronil sulfone was detected at very low concentrations in samples taken at all intervals from all three landscapes.

Conclusions • Washing off landscape hardscapes resulted in pesticide loss

during the intervals analyzed.

• A significant loss of bifenthrin occurred from the 24 h washoff from the “typical” landscape.

– Irrigation over spray would also contribute to the loss of material.

– Location of landscape drains and connected hardscape contributed to runoff.

• Fipronil loss even in the “typical” landscape was less than expected.

Conclusions continued • Adjustments to the landscape design reduced the overall

pesticide load reaching the gutter.

– Relocating or covering hardscape drains might help.

– Redirecting runoff from hardscapes through improved infiltration or towards vegetation.

Future Research • Determine if a delay in washing off (7 days or 14 days)

following treatment would significantly reduce the mobilization of pesticide.

• Analyze all runoff events (wash off and irrigation) in order to calculate the total loss of material over a specific time period.

• Investigate the use of simple mitigation strategies such as covering drains during application, utilizing a pin stream spray technique, and buffer areas.

Thank You County of Orange Watershed and Coastal Resources

California Department of Pesticide Regulation Drs. Michael Rust and Les Greenberg, UCR Entomology

Drs. Jay Gan and Sveta Bondarenko, UCR Environmental Sciences Tammy Majcherek, UC Davis Plant Sciences

UC ANR South Coast Research & Extension Center