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OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

March 2, 2016

PC Code: 103901

MEMORANDUM DP Barcode: 431858

SUBJECT: Sodium Bentazon: Response to BASF’s Comments on the Proposed Mitigation 

Measures for Bentazon Registration Review

FROM: He Zhong, Ph.D., Biologist

Stephen Wente, Ph.D., Biologist

Environmental Risk Branch 1

Environmental Fate and Effects Division (7507P)

THROUGH: Sujatha Sankula, Ph.D., Branch Chief

Greg Orrick, Risk Assessment Process Leader

Environmental Risk Branch 1

Environmental Fate and Effects Division (7507P)

TO: Moana Appleyard, Chemical Review Manager

Linda Arrington, Branch Chief

Risk Management and Implementation Branch V

Pesticide Re-Evaluation Division (7508P)

The purpose of this Environmental Fate and Effects Division (EFED) memo is to address 

BASF’s response to the Proposed Mitigation Measures for Bentazon Registration Review that 

are applicable to the ecological risk assessment for the herbicide sodium bentazon. BASF’s

response included two submitted reports (MRIDs 49821201, 49821202) and comments in a letter 

dated February 1, 2016. In addition, BASF met with the Agency on January 20, 2016 to discuss 

their response. The following is a list of BASF’s comments organized by topic with EFED’s

response following each of BASF’s comments.

1). Spray Drift Buffer Modeling

BASF submitted a report entitled “Determination of Spray Drift Buffers for Protection of 

Terrestrial Non-Target Areas for Bentazon Herbicides” (MRID 49821201), which used the 

AgDRIFT model to calculate spray drift buffers for both aerial and ground applications.

EFED Response: EFED has reviewed the non-GLP AgDRIFT modeling report (MRID 

49821201). EFED concurs with the modeling results for the spray drift buffer zones based on 

the input parameters modeled, especially the droplet volume median diameter (VMD) for ground 

(≥340 μm) and aerial (≥940 μm) spray. EFED recommends that labels include enforceable label 
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language to mandate use of these spray droplet sizes, as relevant, for both ground and aerial 

applications.

2). Proposed Spray Drift Language

BASF proposed specific label statements pertaining to spray drift. Only those statements that 

EFED believes should be modified are presented below. 

For ground applications:

BASF Statement: Apply this product using nozzles which deliver fine-to-medium/coarse 

spray droplets as defined by ASAE standard S-572 and as shown in nozzle 

manufacturer’s catalogs.

EFED Response: The label should not focus on the type of nozzles, but rather on the 

droplet size. The following label language is suggested: 

Use spray equipment producing spray droplets with a volume median diameter 

(VMD) of 340 μm or greater.

BASF Statement: Avoid potential adverse effects to non-target areas by maintaining a 

10-foot buffer between the application area and the closest downwind edge of sensitive 

terrestrial habitats (such as grasslands, forested areas, shelter belts, woodlots, hedgerows, 

riparian areas, and shrub lands).

EFED Response: Note that this statement is acceptable only if spray droplet size 

language similar to that recommended above is adopted. Based on AgDRIFT modeling, 

the 10-ft buffer is adequate only for ground applications using spray droplets with VMD 

≥340 μm.

For aerial applications:

BASF Statement: Use low-drift straight-stream nozzles (D-6 or larger).

EFED Response: Again, the label should not focus on the type of nozzles, but rather on 

the droplet size. The following label language is suggested:

Use spray equipment producing spray droplets with a volume median diameter 

(VMD) of 940 μm or greater.

BASF Statement: Avoid potential adverse effects to non-target areas by maintaining a 

20-foot buffer between the point of direct application and the closest downwind edge of 

sensitive terrestrial habitats (such as grasslands, forested areas, shelter belts, woodlots, 

hedgerows, riparian areas, and shrub lands).

EFED Response: Again this statement is acceptable only if spray droplet size language 

similar to that recommended above is adopted. Based on AgDRIFT modeling, the 20-ft 

buffer is sufficient only for aerial applications using spray droplets with VMD ≥940 μm.

3). Minimum Retreatment Interval Change

BASF Comment: BASF proposes to change the minimum retreatment interval on bentazon 

product labels from 5 days (current minimum) to 7 days.

EFED Response: EFED concurs the changes, but reiterates that the proposed retreatment 
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interval extension alone does not change the bentazon risk picture for birds and mammals based

on the current default foliar half-life assumption of 35 days. (Please see the response under “5). 

Foliar Dissipation Data” section below for additional information needed to potentially modify 

the 35-day foliar half-life assumption.)

4). Water Holding Time Requirement for Rice

BASF Comment: BASF proposes the following agronomic precautionary statement be included 

in the bentazon product labels that contain a rice use section:

“Avoid releasing tailwater immediately after BASAGRAN application.”

EFED Response: To reduce the risk to aquatic plants from use on rice, EFED suggests the 

following enforceable label language for the label: 

“Do not release tailwater until it has been held for at least 4 days after the last bentazon

application.”

5). Foliar Dissipation Data

BASF submitted a report entitled “Calculation of DT50 dissipation times for BAS 351 H –

Bentazone in wheat and pea plants from field trials in the Northern and Southern Zones of 

Europe” (MRID 49821202), which summarizes the DT50 dissipation times obtained from these 

field trials, but does not provide a full description of the materials and methods used to conduct 

the field trials.

EFED Response: The full studies are needed in order to evaluate their usefulness for risk 

assessment. In other words, the original studies should be submitted with a full description of 

the materials and methods (especially the precipitation data, sampling intervals, sample storage

stability, sample recovery, analytical procedures, and quality assurance procedures). The 

submitted summary results (MRID 49821202) for the foliar dissipation half-life may be 

considered if the original studies are classified upon review as acceptable or otherwise useful for 

risk assessment.

References

Jackson, S.H. 2016. Determination of Spray Drift Buffers for Protection of Terrestrial NonTarget Areas for Bentazon Herbicide. MRID 49821201. 18pp

Miles, B. 2016. Calculation of DT50 Dissipation Times for BAS 351 H - Bentazone in Wheat 

and Pea Plants from Field Trials Conducted in the Northern and Southern Zones of 

Europe. MRID 49821202. 86 pp

USEPA. 2014. Registration Review Ecological Risk Assessment and Effects Determination for 

Sodium Bentazon. DP Barcode 417314. 140pp