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.
* 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
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
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.
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
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
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
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