km ReseaKh Noti

SO-255

Streamwater Contamination After

Aerial Application of a Pelletized Herbicide1

James H.,Miller and A. C. Bate, Jr.

SUMMARY .

Concentrations of hexazinone and its metabolites

were monitored in a Piedmont stream for 8 months

after aerial application of a pelletized formulation

(Velpar@ Gridball’“). Downstream water-users and

fish are probably safe from toxic exposure if treatment

areas have only small streams (less than 50 cm average

channel width) and if labeled rates are not exceeded.

Hexazinone concentrations were highest 30 minutes

after application at 2.4 ppm, declining to less than half

at I hour, I. I ppm, and half again at 2 hours, .49 ppm.

No contamination was evident after the Sthday

sampling. Stream contamination from pellets was as

much as 100 times the concentrations reported for

foliar sprays, aerially applied over brush-covered

streams at similar rates.

Additional keywords: hexazinone, VelparB

Gridball TM, chemical silviculture.

’ Use of trade, firm, or corporation names in this publication is

for the information and convenience of the reader. Such use

is not an official endorsement or approval by the U.S.

Department of Agriculture of any product or service to the

exclusion of others that may be suitable.

If herbicides are handled, applied, or disposed of improperly

they may be injurious to humans, domestic animals,

desirable plants, and pollinating insects, fish, or other

wildlife, and may contaminate water supplies. Use herbicides only when needed and handle them with care. Follow

the directions and heed all precautions on the container

label.

INTRODUCTION

Soil-active herbicides in pelleted forms are

gaining increased interest and use in silvicultural

treatments. \?elpar@ Gridball TM, a large pellet of 10

percent active ingredient (a.i.) hexazinone, is now

registered in all southern states for pine release

and site preparation; but its widespread use is

awaiting its widespread availability (Hamilton

1979, Parker 1979). Tordon 1 OK8 (10 percent a.i.

picloram) is commonly applied for kudzu (Pueraria

/ohm) control before reforestation, and further

trials are examining the possible use for chemical

site preparation (Mann and Haynes 1978). Other

pelletized herbicides such as Graslans(20 percent

a.i. tebuthiuron) and Banvel XP@ (10 percent a.i.

dicamba) are now used in tangeland reclamation

(Graslan) and right-of-way control (Banvel XP) and

may become useful in forest management.

Pelleted chemicals are more likely than sprayed

chemicals to land on the target areas because

there is no spray drift. And soil active herbicide

pellets do not need the stringent weather and

foliage conditions required by foliar sprays. So,

favorable application periods would be much

longer than those for aerial sprays. Also, nonindustrial forest landowners could make ground

applications without having to purchase expensive

application equipment. Use of pellets could make

herbicide applications in forestry more environmentally safe and operationally practical.

Southern Forest Experiment Station/T-10210 U.S. Postal Services Bldg.. 701 Loyola Avenue. New Orleans, La. 701 13

Forest Service, U.S. Depsrtment of Agriculture.

Servmg Alabama. Arkansas. Louisiana. Mississippi, Eastern Oklahoma, Tennessee. Eastern Texas
To find how much an aerial application of

pelletized herbicide contaminates streamwater,

we applied Velpar Gridball aerially on a recently

harvested Piedmont watershed. The basal area of

unharvested hardwoods was 3.5 m2/ha (15

ft2/acre). For the next 8 months, we monitored

concentration of hexazinone and its metabolites in

a small stream in the treated area. Also, we studied

joint application of pine seed and the pelletized

herbicide. Such a combination of operations would

help minimize costs of establishing a plantation.

METHODS

On February 23, 1978, a helicopter fitted with a

Simplex Airblown Seeder applied 0.8 kg/ha (3/4

lb/acre) loblolly pine seed coated with arasan, a

bird repellent, and endrin, an animal repellent.

Then, from the same seeder at the largest gate

openings, Velpar Gridball was apblied to a 0.8 ha (2

acre) rectangular plot-66 by 122 m (216 x 400

ft)-extending from ridge to ridge across the valley

(fig. 1); 4.6 percent of the 17.4 ha (43 acre)

watershed was treated. Because of crosswinds,

the treatment plot was flown in four 30.5 m (100 ft)

swaths, 66 m (216 ft) long, parallel to the stream.

One swath was applied directly over the flood

plain, and we saw pellets falling into the stream.

Figure 1 .-Rectangular plot of 0.8 ha aerially treated with 1.8

kg/ha a./. hexar,norle after a selecttve harvesting of

rhe entire 17.4 ha watershed.

The rate of application was 18 kg/ha (16 lb/acre)

Velpar Gridball or 1.8 kg/ha (1 .6 lb/acre) a.i.

hexazinone. We made a pretreatment calibration

of the seeder on an adjacent cleared area by using

“blank” pellets. The stream channel was not over 1

m wide at pools and averaged 30 cm at rills. Herbs

and shrubs grew along the edge, and leafless

hardwoods along the banks provided partial

channel cover.

Streamwater samples were collected and discharge measured at a point immediately

downstream from the treatment plot (fig. 1). One

sample and a measurement were taken after

treatment at 1, 5, 15, and 30 minutes; 1, 2, and 3

hours; 1, 5, 10 and 46 days; and at 8 months.

Polythene bottles were given a final rinse with a

sample before collection. Samples were then kept

frozen until analyses. Using a gas chromatographic

technique and a nitrogen-phosphorus detector, the

Biochemical Department at E. I. duPont

deNemours & Co analyzed residues. This

procedure quantifies hexazinone (3-cyclohexyl-6-

(dimethylamino)- 1 -methyl- 1,3,5-triazine.2.4 (1 H,

3H)-dione) and two of its most prevalent

metabolites - Metabolite A i s 3-(4-

hydroxycyclohexyl)-6-(dimethylamino)- 1 -methyl1,3,5triazine,2,4 (1 H,3H)dione. and Metabolite B

is 3-cyclohexyl-6-(methylamino)-l -methyl-l ,3,5-

triazine-2,4(1 H,3H)dione.

RESULTS AND DISCUSSION

Hexazinone concentrations in streamwater

were highest 30 minutes after application, 2.4

ppm, and declined to less than half at 1 hour, 1.1

ppm, and half again at 2 hours, .49 ppm (fig. 2a).

This concentration pattern is the same as. that

reported by Norris (1967) for a complete aerial

spray application of 2.2 kg.‘ha (2 lb, acre) acid

equivalent (a.e.1 2,4,5-T to a 5-acre watershed in

Oregon’s Coast Range (fig. 26). But stream

contamination froni hexazinone pellets was about

100 times the conceitrations from spray (Norris

1967).

In both cases, contamination resulted mainly

because chemicals were applied directly to the

stream surface. In our study, chances were slight

James H. Miller is Research Forester, Andrews Forestry Sciences Laboralory. Auburn Universlly. Auburn. Alabama. ma~n~;~tned by

the Southern Fores1 Experiment Statton, Forest Service-USDA. A. C. Bate. Jr.. now deceased, was General Manager. Resource

Operations, inc., Birmingham, Alabama.

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(a) PELLETED

HERBICIDE

0 2 4 6 8 IO I2 14 16 18 20 22 24 I20

MOURS AFTER APPLICATION

Figure 2.-(a) Hexazinone concentrations (ppm) after aerial

application of a pellet formulation in Alabama,

(b) 24.5-T concentrations (parts per billion) after

aerial spraying in Oregon (from Norris 1967).

that hexazinone might have reached the stream by

subsurface leaching through the soil, except

where pellets landed close to the stream. In a 9-

month study with 14C labeled material, after heavy

precipitation (191 cm or 75 in) on a silt-loam soil,

hexazinone was leached only to the 30 cm (12 in)

depth (Riggleman 1978). Because our study area

had a clay-loam soil and 75 cm (30 in) of

precipitation during the 8-month sampling period,

downward or lateral leaching was probably much

less than 30 cm.

Contamination might also enter the stream in

surface runoff, which is usually negligible in forest

soils (Hewlett and Nutter 1971). Observations in

selected spots showed that pellets remained in

place on sloping skid-trails and were 80 percent

dissolved within the first 10 days. But, using

analytical techniques with a .02 ppm detection

limit, we found no stream contamination from

hexazinone after the fith-day sample. A 3.6 cm (1.4

in) storm occurred before the 5-day sampling, but

no increase in concentration was caused by

surface runoff or subsurface migration (fig. 2a).

Precipitation was 1.3 cm (9 in) before the lo-day

sampling and 6 cm (2.5 in) before the 46-day

sampling. Neither sampling had detectable hexazinone or its metabolites.

Total placement of hexazinone into the stream

was 4.4 g, equivalent to 12.5 pellets landing in the

water with -35 g a.i. each. We calculated this

amount of loss by integrating concentration and

discharge data. Stream discharge at the time of

treatment was at low flow, .05 I/set (.0018

fV/sec). The loss to streamwater is 1.2 percent of

the herbicide we applied in the swath over the flood

plain. This percentage approximates the percentage of the swath we estimated was occupied by

the stream. So, most contamination resulted from

pellets landing in the stream. One can estimate

total amount of pelleted herbicide that will be

placed in a stream system during a treatment by

multiplying the application rate (kg/ha a.e. or a.i.)

by the estimated surface area (ha) of the stream

channel to be overflown.

Stream-cover interception apparently accounts

for the difference in contamination concentrations

between aerial sprays and pellets. The degree of

contamination from pellets is apparently not

influenced by brush and logging residues

overhanging the stream channel. The foliar sprays

reported by Norris (1967) were applied after full

leaf development in a region with abundant shrub

and herbaceous cover along and over the upland

streams. Generally, low-volume sprays are applied

so that foliar interception will be maximized. But

rounded pellets aerially applied will not be stopped

by foliage and will most likely land on the ground or

in the stream. Therefore, aerial applications of

pellets over a stream represent a greater potential

for contamination than does aerial application of

sprays.

ESTIMATE OF ENVIRONMENTAL HAZARD

The actual hazard of hexazinone contamination

to downstream water-users and aquatic populations depends on peak and sustained concentrations. Peak concentrations are difficult to

estimate since they depend on the rate that the

pellets dissolve, streamflow, and the rate that the

active ingredient is detoxified or adsorbed -by

bottom sediments. Prolonged exposure to a toxic

substance is more hazardous in aquatic en3
vironments than are peak concentrations. Estimates of potential sustained concentrations can

be made from this study’s findings if we assume

sustained concentrations to be additive. Because

this study monitored low-flow conditions, we are

using the most extreme situation with maximum

concentrations for estimating potential environmental hazards.

For every 66 m (218 ft) of flood plain treated in a

watershed, hexazinone contamination would have

a 0.1 ppm increment and would remain at that level

for about 96 hours at the streams’ confluence. As

figure 2a shows, the 0.1 ppm level was reached at

24 hours, and then concentration declined to .04

ppm at 120 hours. The sustained concentrate for

the first 96 hours was about 0.1 ppm.

No-effect levels of hexazinone for commonly

occurring fish species and 96 hour exposures have

been determined2: 370 ppm for bluegill sunfish

(Lepomis macrochirus), 240 ppm for rainbow trout

(Salma gairdner$ and ,160 ppm for fathead

minnow (Pimephales promelas). Here, “no-effect

levels” means the highest concentration having no

visible effects and causing no mortality. The,TLso

(concentrations in the water for 96 hours caustng

50 percent mortality of test fish) for bluegill is

> 370 ppm and < 420 ppm. A reliable estimate for

the Piedmont’s drainage density is 2.4 km perennial stream per 100 ha of land area (4 mi stream per

mi2 land).3 For the most susceptible fish, fathead

minnow, an assured no-effect size of treatment

area within one watershed would be 14440 ha

(10,971 acres). This figure assumes that all

streams are the size treated in this study (C 0.5 m

width) and that larger streams would be avoided

during application. Environmental hazards of such

careful applications appear minimal for indigenous

fish, because operational applications would be

unlikely to treat 4440 ha.

2 Data from Toxicological Information, Hexazinone by Haskell

Laboratory for Toxicology and Industry Medicine. E. I. duPont

deNemours & Co., Elkton, Md.

3 John Hewlett. Personal conversation. School of Forest

Resources, University of Georgia, Athens. Ga.

The potential for levels toxic to humans can only

be estimated from toxicity data on laboratory

animals. No-effect levels for rats and dogs have

been determined as 1000 ppm hexazinonez in

food, ingested daily for 90 days. This no-effect level

was substantiated by numerous clinical tests and

tissue examinations. Because treatment of 4440

ha with hexazinone would result in estimated

concentrations of only 160 ppm for 96 hours, levels

representing threats to human safety would not be

approached in normal forestry practices.

LITERATURE CITED

Hamilton, Ft. A.

1979. A chemical method to reduce hardwood

competition on pine sites. Proc. South. Weed

Sci. Sot. 32:207-211.

Hewlett, J. D., and W. L. Nutter.

1971. The varying source area of streamflow

from upland basins. In Symp. on interdisciplinary aspects of watershed management [Montana State Univ., Bozeman], p.

65-83.

Mann, W. F., and M. J. Haynes.

1978. Status of some new herbicides. U.S.

Dep. Agric. For. Serv. Gen. Tech. Rep. SO-21,

18~. South. For. Exp. Stn., New Orleans, La.

Norris, L. A.

1967. Chemical brush control and herbicide

residues in the forest environment. In: Herbicides and vegetation management i n

forests, ranges, and non-crop lands [Oregon

State Univ., Corvallis], p. 103-l 23.

Parker, J. A.

1979. Control of single oak trees (Quercus sp.)

with hexazinone pellets. Proc. South. Weed

Sci. Sot. 32:213-216.

Riggleman, J. D. _

1978. Basic Properties of “VelparB” weed

killer and its selective use in sugar cane. Proc.

South. Weed Sci. Sot. 31 :141-l 47.

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