Safety to the environment
Extensive long-term field studies confirm - and governments and regulatory authorities, worldwide, agree - that normal use of paraquat in accordance with the approved label instructions does not cause an unacceptable environmental impact. These studies have shown that:
Paraquat is inactive in soilWhen paraquat residues come into contact with the soil the paraquat active ingredient rapidly becomes adsorbed and strongly bound to clay and organic matter in the soil. It becomes biologically inert and as a result it cannot be taken up by plant roots or other organisms. Paraquat treated soils still maintain an active soil ecosystem with no adverse effects on soil microbes, microorganisms and earthworms. Paraquat cannot be released from the soil or re-activated by the application of water or other agrochemicals. All agricultural soils, not only those with high clay content, have a high capacity to absorb paraquat. In most agricultural areas, applications could take place annually for more than 100 years without exceeding the adsorption capacity of just the top two inches of soil.
- In their review report for paraquat the European Commission (EC) noted that there was “very strong adsorption in all the soils tested” (EC, 2003)
- In their Reregistration Eligibility Decision (RED) document, the US Environmental Protection Agency (EPA) concluded that “due to the apparent adsorption strength of paraquat for soil clays, these bound residues do not appear to be environmentally available.” (US EPA, 1997)
Paraquat cannot travel through soilParaquat binds to soils and cannot be 'leached' or travel to contaminate groundwater. This has been confirmed under laboratory conditions and in long term field studies (up to 20 years) involving vastly exaggerated rates of paraquat.
- In their review report for paraquat the EC concluded that “all studies indicate that paraquat is immobile” (EC, 2003)
- In their RED document, the US EPA declared that “paraquat dichloride was shown to be very immobile in soil” (US EPA, 1997)
Paraquat does not accumulate to unacceptable levels in soilBioavailable paraquat is rapidly degraded by soil microorganisms in a matter of days into natural products such as CO2 and water. Since this is an equilibrium process, the net result is that even following repeated applications the levels of paraquat in soil reaches a plateau at an acceptable concentation. This has been demonstrated by long-term field trials, and the paraquat levels declined once the repeated test applications ceased.
- Accumulation studies conducted in the UK and US demonstrated soil residues that were well below the theoretical maximum after 20 and 10 years, respectively. These studies were also considered by the EC in their paraquat review (EC, 2003)
Paraquat does not contaminate ground waterParaquat binds so strongly with clay particles that it cannot be released to contaminate ground water. In fact, it binds so strongly that to release the paraquat from soil samples for analysis in laboratory conditions, the clay particles have to be broken down and destroyed through a boiling process in concentrated acid for several hours.
- In their RED facts document, the US EPA concluded that “paraquat is not expected or considered to be a groundwater concern from normal paraquat dichloride use patterns” (US EPA, 1997)
- In their review report for paraquat the EC observed that “paraquat will not be used under conditions where contamination of (groundwater in) the saturated zone occurs” (EC, 2003)
Paraquat poses no unacceptable risk to earthworms or soil microorganismsSince paraquat is deactivated by soil, the residues of paraquat application also have no harmful effects on earthworms. Likewise it has no significant effect on the micro-biological activity and fertility of the soil. The important biological processes in the soil such as nitrogen and carbon mineralization are not affected.
- In their review report for paraquat, the EC concluded that “No adverse effects were observed on earthworm populations in a field study following application of up to 720 kg as*/ha in one year” (EC, 2003)
* as = active substance
Paraquat is not hazardous to fish in normal useAs with any pesticide it is possible that small amounts of paraquat could enter water through spray drift or when using paraquat to control weeds on the banks of irrigation channels or ditches. Although there is a variation in the toxicity of paraquat to different species of fish there is a big margin of safety between the levels which might accidentally contaminate water during normal use and those which are toxic in studies with 96 hours exposure, even for the most sensitive fish species. Similar studies showed there was no evidence of any unacceptable effects on invertebrates found in natural water systems. In their RED document, the US EPA concluded that “the registered uses of paraquat dichloride are not expected to pose an acute risk to any aquatic organisms” (US EPA, 1997)
Normal use of paraquat poses no unacceptable risk to domestic or farm animalsThere is no unacceptable health risk to domestic animals, which enter fields that have been sprayed with paraquat at normal recommended dilutions or to cattle and sheep if they graze on sprayed vegetation, provided the spray deposit has dried. Studies have shown there is no harmful effect or build-up of paraquat in farm animals that drink water accidentally contaminated by spraying operations.
Normal use of paraquat poses no significant risk to wildlifeForty years of experience and field trials have established that there is no significant risk to wildlife from normal use of paraquat. Residues, even on freshly sprayed vegetation, would not be expected to present a risk to birds. Wild bird populations were monitored over a five-year period on a farm where paraquat use was much higher than usual, including use beneath hedgerows and along fence lines. This very intensive use during the five years did not adversely affect the birds in population density or variety of species on the farm.
- In their RED document, the US EPA concluded that “acute toxicity to terrestrial animals (birds) and mammals only exists immediately after application” (US EPA, 1997)