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Re: Roundup information

Dave Riches wrote:
> 
> <snip>
> 
> I have no experience with your other points, thus am unqualified to
> comment.  However, I would like to point out that glyphosate will
> probably  go down in history as  modern farming's safest and most
> effective single product.  End of story.  

Independent studies show roundup just as bad as the others.  
Glyphosate, Part 2: Human Exposure and 
Ecological Effects. Caroline Cox. Journal of 
Pesticide Reform, Volume 15, Number 4, Winter 
1995. Northwest Coalition for Alternatives to 
Pesticides, Eugene, OR.



Glyphosate, Part 2: Human Exposure and Ecological Effects
by Caroline Cox

OVERVIEW

Residues of the commonly-used herbicide glyphosate have been 
found in a variety of fruits and vegetables. Residues can be 
detected long after glyphosate treatments have been made. 
Lettuce, carrots, and barley planted a year after glyphosate 
treatment contained residues at harvest.

In California, where reporting of pesticide-caused illnesses 
is more comprehensive than in other states, glyphosate 
exposure was the third most commonly-reported cause of 
pesticide illness among agricultural workers. For landscape 
maintenance workers, glyphosate ranked highest.

Glyphosate can drift away from the site of its application. 
Maximum drift distance of 400 to 800 meters (1300-2600 feet) 
have been measured.

Glyphosate residues in soil have persisted over a year.

Although not expected for an herbicide, glyphosate exposure 
damages or reduces the population of many animals, including 
beneficial insects, fish, birds, and earthworms. In some 
cases glyphosate is directly toxic; for example, 
concentrations as low as 10 parts per million can kill fish 
and  1/20 of typical application rates caused delayed 
development in earthworms. In other cases, (small mammals and 
birds, for example) glyphosate reduces populations by 
damaging the vegetation that provides food and shelter for 
the animals.

Glyphosate reduces the activity of nitrogen-fixing bacteria. 
These bacteria transform nitrogen, an essential plant 
nutrient, into a form that plants can use. Glyphosate reduces 
the growth of mycorrhizal fungi, beneficial fungi that help 
plants absorb water and nutrients. Glyphosate also increases 
the susceptibility of plants to diseases, including 
Rhizoctonia root rot, take-all disease, and anthracnose.
-------------------------------------------------------


Glyphosate is a widely-used, broad-spectrum herbicide that is 
used to kill unwanted plants in a wide variety of 
agricultural, lawn and garden, aquatic, and forestry 
situations. It ranks among the top ten herbicides used in the 
U.S., both in agricultural and nonagricultural situations. 
Common brand names are Roundup, Rodeo, Accord, and Vision. 
This is the second part of a summary of glyphosate's hazards. 
Part 1 (JPR 15(3):14-20) discussed the toxicology of 
glyphosate, its breakdown products, and the other ingredients 
in glyphosate-containing products. This part  discusses human 
exposure to glyphosate and its ecological effects.

Human Exposure

The most important ways that people are exposed to glyphosate 
are through workplace exposure (for people who use glyphosate 
products on the job), eating of contaminated food, exposure 
caused by off-target movement following application (drift), 
contact with contaminated soil, and drinking or bathing in 
contaminated water. The next five sections of this factsheet 
summarize information about these five routes of exposure. 
The third section, discussing drift, also covers impacts on 
plants.

Contamination of Food

Analysis of glyphosate residues is "in general laborious, 
complex, and costly."1 For this reason, it is not included in 
government monitoring of pesticide residues in food.1 The 
only information available about contamination of food comes 
from research situations. Such studies demonstrate several 
important points: 

* First, glyphosate can be taken up by plants and moved to 
parts of the plant that are used for food. For example, 
glyphosate has been found in strawberries,2 wild blueberries 
and raspberries,3 lettuce, carrots, barley,4 and fish5,6 
following treatment.

* Second, pre-harvest use of glyphosate on wheat (to dry out 
the grain prior to harvest) results in "significant residues 
in the grain,"1 according to the World Health Organization. 
Bran contains between 2 and 4 times the amount on whole 
grains. Residues are not lost during baking.1

* Third, glyphosate residues can be found in food long after 
treatments have been made. For example, lettuce, carrots, and 
barley contained glyphosate residues at harvest when planted 
a year after treatment.4

Occupational Exposure

Workers in a variety of occupations are exposed to 
glyphosate. Researchers have documented exposure for forestry 
workers in Finland7 and the southeastern U.S., palm 
plantation workers in Malaysia1 and conifer nursery workers 
in Mississippi and Oregon.8 All of these studies generally 
found low, but consistent, exposure rates.

Physicians, however, paint a different picture. In 
California, the state with the most comprehensive program for 
reporting of pesticide-caused illness, glyphosate was the 
third most commonly-reported cause of pesticide illness among 
agricultural workers.9 Among landscape maintenance workers, 
glyphosate was the most commonly reported cause.10 (Both 
these statistics come from reviews of illness reports 
collected between 1984 and 1990.) Even when glyphosate's 
extensive use in California is considered, and the illness 
statistics presented as "number of acute illnesses reported 
per million pounds used in California," glyphosate ranked 
twelfth.9

Drift

In general, movement of a pesticide through unwanted drift is 
"unavoidable."11 Drift of glyphosate is no exception. 
Glyphosate drift, however, is a particularly significant 
problem. Its wide use means that there is a correspondingly 
large potential for drift.12 When drift does occur, "damage 
is likely to be much more extensive and more persistent than 
with many other herbicides."13 This is because glyphosate 
translocates (moves) within plants readily so that even 
unexposed parts of a plant can be damaged. Damage to 
perennial plants (when not exposed to enough glyphosate to 
kill them) is persistent, with some symptoms lasting several 
years.13 In  addition, plant susceptibility varies widely. 
Some wildflowers are almost a hundred times more sensitive 
than others; small amounts of drift will damage these 
species.14

A fundamental question about drift is "How far can I expect 
glyphosate to travel off-site?" Unfortunately, the question 
is difficult to answer, since drift is "notoriously 
variable."15 Factors that increase drift are aerial 
application techniques, high wind speeds (over 10 kilometers, 
or 6 miles, per hour), spray nozzles that produce a high 
proportion of fine droplets, and calm conditions (without 
enough turbulence to drive the glyphosate droplets onto plant 
foliage).15 Drift distances that have been measured for the 
major application techniques include the following:

* Ground Applications: Between 14 and 78 percent of 
glyphosate applied as ground sprays moves off-site.15 
Seedling mortality has been demonstrated 20 meters (66 feet) 
downwind when using a tractor-mounted sprayer. Sensitive 
species were killed at 40 meters (131 feet).16 Models 
indicate that even more sensitive species would be killed at 
distances approaching 100 meters (328 feet).14 Glyphosate 
residues have been measured 400 meters (1312 feet) downwind 
from ground applications.17

* Helicopter applications: Between 41 and 82 percent of 
glyphosate applied from helicopters moves off the target 
site.15 Two studies done in Canada18,19 measured glyphosate 
residues 200 meters (656 feet) from target areas following 
helicopter applications to forest sites. In both studies, 200 
meters was the farthest distance at which samples were taken, 
so the longest distance glyphosate travelled is not 
known.18,19 A third study (from California) found glyphosate 
800 meters (2624 feet) downwind following a helicopter 
application. Again, this was the farthest distance at which 
measurements were made. Plant injury was recorded 400 meters 
(1312 feet) downwind.17

Fixed-wing aircraft: Long drift distances occur following 
applications of glyphosate made from fixed-wing airplanes. 
Three studies on forested sites conducted by Agriculture 
Canada (the Canadian agricultural ministry) showed that 
glyphosate was consistently found at the farthest distance 
from the target areas that measurements were made (200, 300, 
and 400 meters, or  656, 984, and 1312 feet).20-22 A 
California study found glyphosate 800 meters downwind of an 
airplane application. Again, this was the farthest distance 
at which measurements were made. Plant injury was observed at 
100 meters (328 feet). Unlike the first three studies, this 
study used a grass field as the test site.17

One of the Canadian studies22 calculated that buffer zones of 
between 75 and 1200 meters (246 feet - 0.75 miles) would be 
required to protect nontarget vegetation.

Soil Contamination

Persistence: Glyphosate's persistence in soil varies widely, 
so giving a simple answer to the question "How long does 
glyphosate persist in soil?" is not possible. Half-lives (the 
time required for half of the amount of glyphosate applied to 
break down or move away) as low as 3 days and as long as 141 
days have been measured by glyphosate's manufacturer.4 
Initial degradation (breakdown) is faster than the subsequent 
degradation of what remains, resulting in long persistence.23 
Long persistence has been measured in the following studies: 
55 days on an Oregon Coast Range forestry site24; 249 days on 
Finnish agricultural soils25; between 259 and 296 days on 
eight Finnish forestry sites23; 335 days on an Ontario 
(Canada) forestry site26; 360 days on 3 British Columbia 
forestry sites27;  and,  from 1 to 3 years on eleven Swedish 
forestry sites.28 These are minimum estimates because, in all 
but two of these studies, glyphosate was detected on the last 
date samples were analyzed.

Glyphosate is thought to be "readily bound to many soils and 
clay minerals"1  and therefore "immobile or slightly immobile 
in many soils."1  This means that the glyphosate will be 
unlikely to move away from the application site and 
contaminate water or soil elsewhere. However, a new study29 
paints a different picture. The researchers found that 
glyphosate bound readily to the four soils studied. However, 
desorption, when glyphosate unbinds from soil particles, also 
occurred readily. In one soil, 80 percent of the added 
glyphosate desorbed in a two hour period. The study concludes 
that "this herbicide can be extensively mobile in the soil 
environment.."29

Water Contamination

Based on the prevailing view that glyphosate binds readily to 
soil particles, it does not have the chemical characteristics 
of a pesticide that is likely to leach into either ground or 
surface water.1 (If it readily desorbs, as described above, 
this picture would change.) In either case, glyphosate can 
move into surface water when the soil particles to which it 
is bound are washed into streams or rivers.4 How often this 
happens is not known, because routine monitoring for 
glyphosate in water is infrequent.1

However, glyphosate has been found in both ground and surface 
water. Examples include two farm ponds in Ontario, Canada, 
contaminated by run-off from an agricultural treatment (one 
pond) and a spill (the other pond)30; the run-off from a 
watersheds treated with Roundup during production of no-till 
corn and fescue31; contaminated surface water in the 
Netherlands1; and seven U.S. wells (one in Texas, six in 
Virginia) contaminated with glyphosate.32

Glyphosate's persistence in water is shorter than its 
persistence in soils. Two Canadian studies found glyphosate 
persisted 12 to 60 days in pond water following direct 
application.33,34 Glyphosate persists longer in sediments. 
For example, a study of Accord applied to forest ponds found 
glyphosate residues in sediment 400 days after application.1 
The half-life in pond sediments in a Missouri study was 120 
days; persistence was over a year in pond sediments in 
Michigan and Oregon.4

Ecological Effects

Glyphosate can  impact many organisms not intended as targets 
of the herbicide. The next two sections describe both direct 
mortality and indirect effects, through destruction of food 
or shelter. 

Effects on Nontarget Animals

Beneficial insects: Glyphosate-containing products pose 
hazards to insects that are economically beneficial because 
they  kill pest insects. The International Organization for 
Biological Control found that exposure to freshly dried 
Roundup killed over 50 percent of three species of beneficial 
insects: a parasitoid wasp, a lacewing, and a ladybug.35 Over 
80 percent of a fourth species, a predatory beetle, was 
killed. 

Similar impacts on beneficial insects have been shown in 
field studies. In North Carolina winter wheat fields, 
populations of large carabid beetles declined after treatment 
with a commercial glyphosate product and did not recover for 
28 days.36 A study of Roundup treatment of pasture hedgerows 
in the United Kingdom showed a similar decline in carabid 
beetles.37

Roundup treatment of a Maine clear-cut caused an 89 percent 
decline in the number of herbivorous (plant-eating) insects. 
While these are not usually considered beneficial insects, 
they serve as an important food resource for birds and 
insect-eating small mammals.38

Aquatic insects can also be affected by glyphosate. Midge 
larvae (important food for breeding waterfowl39) are killed 
by glyphosate in amounts that vary widely. For example, one 
study found that 55 parts per million (ppm) of glyphosate 
killed midge larvae6 while other studies found that 65040 
-560039 ppm of Rodeo (containing glyphosate and water) were 
required to kill the larvae. Part of the variability is 
related to water hardness.39

The U.S. Fish and Wildlife Service has identified one 
endangered species of insect, a longhorn beetle, that would 
be jeopardized by use of glyphosate.41

Other arthropods: Glyphosate and glyphosate-containing 
products kill a variety of other arthropods. For example, 
over 50 percent of test populations of a predatory mite that 
is an important predator of pest mites was killed by exposure 
to Roundup.35 In another laboratory study, Roundup exposure 
caused a decrease in survival and a decrease in body weight 
of woodlice. These arthropods are important in humus 
production and soil aeration.42 Roundup treatment of pasture 
hedgerows reduced the number of spiders, probably by killing 
the plants they preferred for web-spinning.37 The water flea 
Daphnia pulex is killed by concentrations of Roundup between 
3 and 25 ppm.6,43,44 Young Daphnia are more susceptible than 
mature individuals, and suspended sediments in the water 
increased the toxicity.43 The red swamp crawfish, a 
commercial species, was killed by 47 ppm of Roundup.45

Fish: Both glyphosate and the commercial products that 
contain glyphosate are acutely toxic to fish. In general, 
glyphosate alone is less toxic than the common glyphosate 
product, Roundup, and other glyphosate products have 
intermediate toxicity. Part of these differences in toxicity 
to fish can be explained by the toxicity of the surfactant 
(detergent-like ingredient) in Roundup. It is about 30 times 
more toxic to fish than glyphosate itself.44

Acute toxicities of glyphosate vary widely: median lethal 
concentrations (LC50s; the concentrations killing 50 percent 
of a population of test animals) from 10 ppm to over 1000 ppm 
have been reported depending on the species of fish and test 
conditions.1 In soft water there is little difference between 
the toxicities of glyphosate and Roundup.

Acute toxicities of Roundup to fish range from an LC50 of 3.2 
ppm to an LC50 of 52 ppm.1 Acute toxicities of Rodeo (used 
with the surfactant X-77 per label recommendations) vary from 
120 to 290 ppm.46

Factors important in determining the toxicity of glyphosate 
or glyphosate-containing products to fish include the 
following: 

* First, different species of fish have different 
susceptibilities. For example, coho and chinook salmon are 
more tolerant of glyphosate than pink or chum salmon.47

* Water quality is important: glyphosate in soft water was 20 
times more toxic to rainbow trout than was glyphosate in hard 
water. For Roundup, the reverse is true: it is more toxic in 
hard water than in soft.47,48

* Age affects the susceptibility of fish because juveniles 
are often more susceptible than adults.  For example, Roundup 
was four times more toxic to rainbow trout fry and 
fingerlings than it was to larger fish.6

* Nutrition also can determine toxicity. Hungry fish are more 
susceptible to glyphosate than fed fish. For example, fed 
flagfish were 10 times more tolerant of glyphosate than unfed 
fish.49

* Finally, glyphosate toxicity increases with increased water 
temperature. In both rainbow trout and bluegills, toxicity 
about doubled between 7 and 17!C (45 and 63!F).6 Treatment of 
riparian areas with glyphosate causes water temperatures to 
increase for several years following treatment50 because the 
herbicide kills shading vegetation. This means that repeated 
use of glyphosate in a watershed could favor its increased 
toxicity to fish. In addition, the temperature increase 
itself could be critical for fish, like juvenile salmon, that 
are sensitive to water temperature.

Sublethal effects of glyphosate on fish are also significant 
and occur at low concentrations. Studies of rainbow trout and 
Tilapia found that concentrations of about 1/2 and 1/3 of the 
LC50 (respectively) caused erratic swimming.51,52 The trout 
also exhibited labored breathing.51 Behavioral effects can 
increase the risk that the fish will be eaten, as well as 
affecting feeding, migration, and reproduction.52

Birds: Glyphosate is acutely toxic to birds, but only in 
large amounts. The LC50, the amount in food that kills 50 
percent of a population of test animals, is often above 4000 
milligrams per kilogram of food.1

Glyphosate also has indirect impacts on birds. Because 
glyphosate kills plants, its use creates a dramatic change in 
the structure of the plant community. This affects bird 
populations, since the birds depend on the plants for food, 
shelter, and nest support. 

For example, a study of four glyphosate-treated clear-cuts 
(and an unsprayed control plot) in Nova Scotia found that the 
densities of the two most common species of birds (white-
throated sparrow and common yellowthroat) decreased for two 
years after glyphosate treatment. By the fourth year post-
spray, densities had returned to normal for these two 
species. However, the unsprayed plot had by then been 
colonized by new species of birds (warblers, vireos, and a 
hummingbird). These species did not appear on the sprayed 
plots.53

An earlier three year study of songbird abundance following 
glyphosate treatment of clear-cuts in Maine forests showed 
similar results. Abundances of the total number of birds 
(Figure 2) and three common species decreased. The decrease 
in bird abundance was correlated with decrease in the 
diversity of the habitat.54

Black grouse avoided glyphosate-treated clear-cuts in Norway 
for several years after treatment.55 Researchers recommended 
that the herbicide not be used near grouse courtship areas.

Small mammals: In field studies, small mammals have also been 
indirectly affected when glyphosate kills the vegetation they 
(or their prey) use for food or shelter. This was first shown 
in studies of clear-cuts in Maine.38 Insect-eating shrews 
declined for three years post-treatment; plant-eating voles 
declined for two. A second study in Maine56 found similar 
results for voles, but not shrews. A British Columbia study 
found that deer mice populations were dramatically (83 
percent) lower following glyphosate treatment.57 While some 
other studies have found no affect on mice, this may have 
occurred because treated areas were small.1 This suggests 
that effects are more severe when large areas are treated. 

In Norway, there was a "strong reduction" in use of sprayed 
clear-cuts by mountain hare.58 

Earthworms: A study of the most common earthworm found in 
agricultural soils in New Zealand showed that glyphosate 
significantly affects growth and survival of earthworms. 
Repeated biweekly applications of low rates of glyphosate 
(1/20 of typical rates) caused a reduction in growth, an 
increase in the time to maturity, and an increase in 
mortality.59

Effects on Nontarget Plants

As a broad-spectrum herbicide, glyphosate has potent acutely 
toxic effects on most plant species. However, there are other 
kinds of serious effects. These include effects on endangered 
species, reduction in the ability to fix nitrogen, increased 
susceptibility to plant diseases, and reduction in the 
activity of mycorrhizal fungi.

Endangered species: Because essentially all plants are 
susceptible to glyphosate-caused damage or mortality, 
glyphosate can seriously impact endangered plant species. The 
U.S. Fish and Wildlife Service has identified 74 endangered 
plant species that it believes could be jeopardized by use of 
glyphosate. This list is based on the use of glyphosate on 9 
crops, and does not include over 50 other uses.41

Nitrogen fixation: Nitrogen is important because of its "near 
omnipresence" in membranes, proteins, and genetic material of 
living things. Most living things cannot use nitrogen in its 
common form and instead use ammonia and nitrates, much rarer 
compounds. The processes by which ammonia and nitrates are 
created are called nitrogen fixation and nitrification. They 
are carried out by certain bacteria.60

A number of studies (from Iowa,61 Australia,62 eastern 
Canada,63 and Ontario (Canada)64,65) have shown that 
commercial glyphosate products can reduce nitrogen-fixing or 
nitrification activity of soils. The amount of glyphosate 
that produces inhibitory effects varies  from 262 to 200063 
ppm. Effects can be persistent; the formation of nitrogen-
fixing nodules on clover roots was inhibited 120 days after 
treatment. 62

In addition, tests of cultured nitrogen-fixing bacteria have 
also shown that glyphosate inhibits nitrogen-fixation. These 
studies included the nitrogen-fixing species in roots of 
soybeans66 and clover.67-68

Given the importance of nitrogen-fixation to agriculture, 
more research is crucial.

Mycorrhizal fungi: Mycorrhizal fungi are beneficial fungi 
that live in and around plant roots. They help plants absorb 
nutrients and water and can  protect them from cold and 
drought.69 Glyphosate is toxic to many species of mycorrhizal 
fungi. Effects, mostly growth inhibition, have been observed 
at concentrations between 1 and 100 ppm.70-73 

Plant diseases: Glyphosate treatment increases the 
susceptibility of crop plants to a number of diseases. For 
example, glyphosate reduced the ability of bean plants to 
defend themselves against the disease anthracnose.74 
Glyphosate increased the growth of take-all disease in soil 
from a wheat field. In addition, the proportion of soil fungi 
which was antagonistic to the take-all fungus decreased.75 
Bean seedlings also survived glyphosate treatment when grown 
on sterile soil, but not when grown on normal (not 
sterilized) soil.76 Spraying of Roundup prior to planting 
barley increased the severity of Rhizoctonia root rot and 
decreased barley yield.77 In addition, Roundup injection of 
lodgepole pine inhibited the defensive response of the tree 
to blue stain fungus.78  

References

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Programme, International Labour Organization. 1994. 
Glyphosate. Environmental Health Criteria #159. Geneva, 
Switzerland.

 2. Cessna, A.J. and N.P. Cain. 1992. Residues of glyphosate 
and its metabolite AMPA in strawberry fruit following spot 
and wiper applications. Can. J. Plant Sci. 72: 1359-1365.

 3. Roy, D.N. et al. 1989. Uptake and persistence of the 
herbicide glyphosate (Vision?) in fruit of wild blueberry and 
red raspberry. Can. J. For. Res. 19: 842-847.

 4. U.S. EPA. Office of Pesticide Programs. Special Review 
and Reregistration Division. 1993. Reregistration eligibility 
decision (RED): Glyphosate. Washington, D.C. (September.)

 5. Wang, Y., C. Jaw, and Y. Chen. 1994. Accumulation of 2,4-
D and glyphosate in fish and water hyacinth. Water Air Soil 
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 6. Folmar, L.C., H.O. Sanders, and A.M. Julin. 1979. 
Toxicity of the herbicide glyphosate and several of its 
formulations to fish and aquatic invertebrates. Arch. 
Environ. Contam. Toxicol. 8:269-278.

 7. Jauhiainen, A., et al. 1991. Occupational exposure of 
forest workers to glyphosate during brush saw spraying work. 
Am. Ind. Hyg. Assoc. J. 52(2):61-64.

 8. Lavy, T.L. et al. 1993. Measurements of year-long 
exposure to tree nursery workers using multiple pesticides. 
Arch. Environ. Contam. Toxicol. 24:123-144.

 9. Pease, W.S. et al. 1993. Preventing pesticide-related 
illness in California agriculture: Strategies and priorities. 
Environmental Health Policy Program Report. Berkeley, CA: 
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10. Robinson, J.C. et al. 1994. Pesticides in the home and 
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Environmental Health Policy Program Report. Berkeley, CA: 
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11. Ware, G.W. et al. 1983. Reducing pesticide application 
drift-losses. Tucson, AZ: University of Arizona. College of 
Agriculture. Cooperative Extension Service.

12. Payne, N.J. 1992. Off-target glyphosate from aerial 
silvicultural applications and buffer zones required around 
sensitive areas. Pestic. Sci. 34:1-8.

13. Atkinson, D. 1985. Glyphosate damage symptoms and the 
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14. Breeze, V., G. Thomas, and R. Butler. 1992. Use of a 
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15. Freedman, B. 1990-1991. Controversy over the use of 
herbicides in forestry, with particular reference to 
glyphosate usage. J. Envir. Sci. Hlth. C8(2):277-286.

16. Marrs, R.H. et al. 1993. Determination of buffer zones to 
protect seedlings of non-target plants from the effects of 
glyphosate spray drift. Agric. Ecosys. Environ. 45:283-293.

17. Yates, W.E., N.B. Akesson, and D.E. Bayer. 1978. Drift of 
glyphosate sprays applied with aerial and ground equipment. 
Weed Sci. 26(6):597-604.

18. Riley, C.M., C.J. Weisner, and W.A. Sexsmith. 1991. 
Estimating off-target spray deposition on the ground 
following the aerial application of glyphosate for conifer 
release in New Brunswick. J. Environ. Sci. Health B26(2):185-
208.

19. Payne, N.J., J.C. Feng, and P.E. Reynolds. 1990. Off-
target depositions and buffer zones required around water for 
aerial glyphosate applications. Pestic. Sci. 30:183-198.

20. Payne, N.J. and D.G. Thompson. 1992. Off-target 
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under various meteorological conditions. Pestic. Sci. 34:53-
59.

21. Payne, N.J. 1993. Spray dispersal from aerial 
silvicultural applications. Crop Protec. 12(6):463-469.

22. Payne, N.J. 1992. Off-target glyphosate from aerial 
silvicultural applications, and buffer zones required around 
sensitive areas. Pestic. Sci. 34:1-8.

23. Torstensson, L. and Stark, J. 1979. Persistence of 
glyphosate in forest soils. In Weeds and weed control. 20th 
Swedish Weed Conference. Uppsala. 31 January - 2 February 
1979. Uppsala, Sweden: Swedish University of Agricultural 
Sciences.

24. Newton, M. et al. 1984. Fate of glyphosate in an Oregon 
forest ecosystem. J. Agric. Food. Chem. 32:1144-1151.

25. Mller, M. et al. 1981. Fate of glyphosate and its 
influence on nitrogen-cycling in two Finnish agricultural 
soils. Bull. Environ.. Contam. Toxicol. 27:724-730.

26. Feng, J.C. and D.G. Thompson. 1990. Fate of glyphosate in 
a Canadian forest watershed. 2. Persistence in foliage and 
soils. J. Agric. Food. Chem. 38: 1118-1125.

27. Roy, D.N. et al. 1989. Persistence, movement, and 
degradation of glyphosate in selected Canadian boreal forest 
soils. J. Agric. Food. Chem. 37:437-440.

28. Torstensson, N.T.L., L.N. Lundgren, and J. Stenstrm. 
1989. Influence of climate and edaphic factors on persistence 
of glyphosate and 2,4-D in forest soils. Ecotoxicol. Environ. 
Safety 18:230-239.

29. Piccolo, A. et al. 1994. Adsorption and desorption of 
glyphosate in some European soils. J. Environ. Sci. Health 
B29(6): 1105-1115. 

30. Frank, R. et al. 1990. Contamination of rural ponds with 
pesticide, 1971-1985, Ontario, Canada. Bull. Environ. Contam. 
Toxicol. 44:401-409.

31. Edwards, W.M., G.B. Triplett, Jr., and R.M. Kramer. 1980. 
A watershed study of glyphosate transport in runoff. J. 
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Follow-Ups: References: