Forest Chemicals and Water Quality: Conclusions from Watershed Studies using Modern BMPs. Vickie Tatum NCASI SRM June 21, 2016

Transcription

1 Forest Chemicals and Water Quality: Conclusions from Watershed Studies using Modern BMPs Vickie Tatum NCASI SRM June 21, 2016

2 Which Studies? Three studies designed to evaluate the effectiveness of modern BMPs and application techniques for reducing movement of herbicides away from the site of application and into nearby water bodies. Needle Branch (Oregon) Alto (East Texas) Dry Creek (South Georgia)

3 Which Studies? McBroom, Matthew W., et al. "Runoff of silvicultural herbicides applied using best management practices." Forest Science 59.2 (2013): Scarbrough, S. Lynsey, et al. "Herbicide concentrations in first-order streams after routine application for competition control in establishing pine plantations." Forest Science 61.3 (2015): Louch, Jeff, et al. "Potential risks to freshwater aquatic organisms following a silvicultural application of herbicides in Oregon's Coast Range." Integrated environmental assessment and management (2016).

4 Study Site Characteristics Site Characteristic Description Steep sloped, V- shaped drainage Needle Branch (OR) Alto (TX) Dry Creek (GA) Rolling hills, flat floodplains associated w/ larger streams Watershed # Watershed Size 70 ha Small: 2.5 ha Large: ha Soil Types Baseflow? Well drained loams, gravelly loams Yes, but summer flows low, can be discontinuously perennial Mostly fine-textured sand/sandy loams over clay No 1: moderately incised V-shaped valley 2: weakly defined w/in riparian wetland 1: 33.3 ha 2: 44.1 ha Mostly well-drained sands/loamy sands over clay/sandy loams Yes

5 What BMPs? SMZs SMZ Harvest None Herbicide Application Needle Branch Alto Dry Creek Minimum 15 m each side fish-bearing lower portion, none along nonfish-bearing upper portion No-spray buffer zone of 18 m each side of fishbeating lower portion; half-boom spraying along non-fish-bearing upper portion Minimum of 15 m each side of perennial, intermittent, & welldefined ephemeral Partial, retention of at least 11.5 m 2 /ha basal area No application in SMZs 12 m on slopes <20%, 21 m on slopes of 21-40% None in upstream half; partial, retention of at least 11.5 m 2 /ha basal area downstream half No application in SMZs

6 Herbicide Applications Needle Branch Site Prep: Accord XRT (glyphosate) + Chopper Gen2 (imazapyr) + Sulfomet Extra (sulfometuron methyl, metsulfuron methyl) Alto Site prep: Arsenal (imazapyr) + Accord (glyphosate) HWC: Oustar (hexazinone, sulfometuron methyl) Release: Arsenal (imazapyr) Dry Creek Site Prep: Chopper (imazapyr) HWC: Oustar (hexazinone, sulfometuron methyl)

7 Herbicide Application Rates (kg/ha) Herbicide Needle Branch Alto Dry Creek Glyphosate Not applied Hexazinone Not applied Imazapyr ,4 Metsulfuron Methyl Not applied Not applied Sulfometuron Methyl Aerial application (helicopter) 2 Ground application (backpack sprayer) 3 Banded ground application (backpack sprayer) 4 Ground application (skidder-mounted sprayer)

8 Sample Collection Details differ somewhat, but basically, autosamplers were triggered by storm events that produced runoff, multiple samples for analysis were collected over the course of the storm event

9 Maximum Single-sample Concentrations of Herbicides in Stream Water at each of the Three Study Sites Herbicide Concentration (µg/l) Herbicide Needle Branch Alto Dry Creek Glyphosate Not applied Hexazinone Not applied Imazapyr < Metsulfuron Methyl Sulfometuron Methyl <1.0 Not applied Not applied <

10 Comparison to Results of Other Forestry Herbicide Field Studies Most older studies not comparable Many set up as unrealistic worst-case scenarios No SMZs Above label max application rates Direct application over water Some used non-operational application methods

11 Comparison to Results of Other Forestry Herbicide Field Studies Compared to previous studies in which herbicides used, application rates, and application methods were relevant to the current studies At Needle Branch, Alto and Dry Creek Application rates tended to be lower No-spray buffer zones tended to be wider Maximum water concentrations of herbicides tended to be lower In some cases, by one or more orders of magnitude

12 Comparison to Results of Other Forestry Herbicide Field Studies Pattern of herbicide movement consistent with previous studies Baseflow concentrations near or below analytical limits Maximum herbicide concentrations in stream water occur immediately following application or during the first storm event Concentrations decrease with each subsequent storm event By the fourth or fifth post-application event (often sooner), herbicide concentrations fall below detectable limits

13 Risk Assessment In order to assess the potential risk to aquatic organisms from movement of forestry herbicides into streams, we need to know: Magnitude of exposure Duration of exposure

14 Duration of Exposure Some data gaps exist due to sampling design Storm event-triggered sample collection often ended before herbicide concentrations returned to background (pre-storm) levels Overall, pulses of elevated herbicide concentrations were relatively short-lived (<24 hours)

15 Using Risk Quotients (RQs) in Risk Assessment RQs are used by EPA for screening level risk assessments in the pesticide registration and registration review processes. If potential issues are identified, then there is additional assessment and analysis

16 Using Risk Quotients (RQs) in Risk Assessment An RQ is the ratio of a model-predicted expected environmental concentration (EEC) to acute and chronic toxicity values for the most sensitive organisms that have been identified in toxicity testing. RQ aquatic organism = water concentration of herbicide/toxicity value If concentration<toxicity value, then the bigger the difference between concentration and toxicity value, the smaller the RQ

17 Toxicity Values used in RQ Calculation for Screening Risk Assessments for Freshwater Organisms Organism Type of Assessment Toxicity Value Aquatic animals Acute Lowest tested EC 50 or LC 50 for freshwater fish and invertebrates in acute toxicity tests Aquatic animals Chronic Lowest NOEC for freshwater fish and invertebrates in early life stage or full life cycle tests Aquatic plants Acute or chronic Lowest EC 50 for both vascular plants and algae EC 50 = Concentration that cause some specified effect in 50% of test organisms LC 50 = Concentration that causes 50% mortality in test organisms NOEC = Highest test concentration that has no effect on test organisms

18 Using Risk Quotients (RQs) in Risk Assessment RQs are then compared to a series of defined Levels of Concern (LOC) to analyze potential risks and guide possible regulatory actions.

19 Some RQs and Corresponding LOCs used by EPA for Screening Risk Assessments RQ Type RQ Value LOC Acute aquatic animals >0.5 Potential for acute risk to non-target organisms that may warrant regulatory action (e.g., use restrictions, mitigation measures) Acute endangered species aquatic animals >0.05 Endangered species may be potentially affected by use Chronic all animals >1 Potential for chronic risk may warrant regulatory action, endangered species may potentially be affected through chronic exposure Acute/Chronic Nonendangered or Endangered Plants >1 Potential effects in endangered plants

20 Site Specific RQs Instead of using modeled EECs to calculate RQs, use actual herbicide concentrations in stream water from forestry field studies Still a conservative assessment Use maximum single-sample concentrations Peak exposure duration in real life much shorter than exposures used in toxicity testing from which toxicity values are derived

21 Glyphosate RQs Calculated using Toxicity Values for the Most Sensitive Species and the Peak Glyphosate Concentration Reported in the Alto Study RQ Type Acute aquatic animals Acute endangered species aquatic animals Chronic all animals Acute/Chronic Nonendangered or Endangered Plants RQ (fish) (amphibian) (aquatic invertebrate) (fish) (amphibian) (aquatic invertebrate) (fish) (aquatic invertebrate) (algae) (macrophyte) RQ Value that Reaches a LOC >0.5 >0.05 >1 >1

22 Imazapyr RQs Calculated using Toxicity Values for the Most Sensitive Species and the Peak Imazapyr Concentration Reported in the Alto Study and, for Macrophytes, Dry Creek RQ Type Acute aquatic animals Acute endangered species aquatic animals Chronic all animals Acute/Chronic Nonendangered or Endangered Plants RQ (fish) (amphibian) (aquatic invertebrate) (fish) (amphibian) (aquatic invertebrate) (fish) (aquatic invertebrate) (algae) 0.74 (macrophyte, Dry Creek) 3.97 (macrophyte, Alto) RQ Value that Reaches a LOC >0.5 >0.05 >1 >1

23 Hexazinone RQs Calculated using Toxicity Values for the Most Sensitive Species and the Peak Imazapyr Concentration Reported in the Alto Study RQ Type Acute aquatic animals Acute endangered species aquatic animals Chronic all animals Acute/Chronic Nonendangered or Endangered Plants RQ (fish) (amphibian) (aquatic invertebrate) (fish) (amphibian) (aquatic invertebrate) (fish) (aquatic invertebrate) 4.40 (algae) (macrophyte) RQ Value that Reaches a LOC >0.5 >0.05 >1 >1

24 Sulfometuron RQs Calculated using Toxicity Values for the Most Sensitive Species and the Peak Sulfometuron Concentration Reported in the Alto Study and, for Aquatic Plants, the Peak Concentration Reported in the Dry Creek Study RQ Type Acute aquatic animals Acute endangered species aquatic animals Chronic all animals Acute/Chronic Nonendangered or Endangered Plants RQ (fish) (amphibian) (aquatic invertebrate) (fish) (amphibian) (aquatic invertebrate) (fish) (aquatic invertebrate) 0.54 (algae - Alto) 0.27 (algae Dry Creek) (macrophyte - Alto) (macrophyte Dry Creek) RQ Value that Reaches a LOC >0.5 >0.05 >1 >1

25 Site-Specific RQ Summary No risks to aquatic invertebrates, fish, or amphibians were identified, but the RQs indicate that potential risks to aquatic plants do exist

26 Is Toxicity to Aquatic Plants Likely to be an Issue in Actual Practice? Are sensitive plants present in areas of streams where peak herbicide values are found? Toxicity tests from which toxicity values are derived use 5-14 days of continuous exposure. Peak exposures in streams measured in hours, not days Studies have shown that short exposures to very high concentrations can be tolerated A study exploring this is in the NCASI Technical Studies Program Toxicity endpoint most commonly used is growth inhibition Studies have shown that as long as the plant is not killed, growth generally rebounds rapidly once herbicide exposure ends

27 Conclusion Overall, the low exposure levels and short exposure durations reported in the three studies described here suggest that use of herbicides in forestry according to modern BMPs poses minimal risk to non-target aquatic animals. A greater potential of risk to non-target plants exists due to the greater sensitivity of plants to herbicides, however, this potential for risk may be mitigated by the very brief exposures to peak concentrations and the pattern of pulsed, rather than continuous, exposures.