Miljøprojekt, 999 – Udarbejdelse af praktiske retningslinier for forebyggelse af forurening af små vandforsyninger i forbindelse med håndtering af pesticider i landbruget

Guidelines for Prevention of Pollution in Small Waterworks - Handling of Pesticides in Agriculture

Summary and conclusions

In this report, the Danish Institute of Agricultural Sciences (DIAS), the Danish Agricultural Advisory Service, Hardi International A/S and Cowi A/S have elucidated risks regarding filling and cleaning of sprayers. The report describes a number of recommendations for improving the handling of sprayers.

The report is the outcome of a project initiated and financed by the Danish Environmental Protection Agency (Danish EPA) in 2001 based on new knowledge obtained during recent years about point source pollution at places where sprayers are filled and cleaned inappropriately. The Danish EPA has asked for an elucidation of the problem and solutions in order to avoid point source pollution in the future.

The project identified and described occasions when the handling of sprayers leads to point source pollution and how these situations could be avoided. Farm checks by the Advisory Service have exposed a widespread practice where the filling of sprayers is carried out on gravel with a risk of drainage to the water environment.

A significant part of the report deals with sorption and degradation of pesticides in biobeds investigated in the project. A full-scale model biobed was established at Flakkebjerg, and the capability of the biobed to retain and degrade pesticides was studied. A substantial reduction in the risk of water pollution is acheived when using a biobed instead of filling and cleaning on bare soil. Leaching and degradation of 21 pesticides were studied, and 13 compounds were not detected in the leachate from the biobed. 8 pesticides were detected, and bentazone gave the highest concentrations. 11% of the bentazone applied was recovered in the leachate. For the rest of the compounds, less than 2% was recovered in the leachate after six months. The undetected compounds were primarily sorbed on the uppermost 10 cm of the biobed material. Strong sorption means reduced bioavailability and longer degradation time, but after six months all compounds were degraded to less than 50% of initial dose (5 g each). Synthetic pyrethroids, which are very hazardous for the water environment, were not covered by the investigation, but literature values of sorption properties indicate very strong sorption to biobed material. A biobed would be a suitable system for handling sprayers with these compounds. It is recommended that the biobed material is replaced every 6-8 years and that the used biobed material is spread over the field. It is estimated that, even in the worst case, pesticide concentration would be below 1 mg pr kg. The biobed is especially suitable on farms with few cleanings in the spraying season or with cleaning in the field.

Filling of sprayer tanks consists in filling with water and filling with pesticide. When filling with water, there is a risk of overflow or foaming. Without a non-return valve, there is also a risk of back running in the water distribution system. This report recommends a non-return valve or filling from a separate tank with a volume preventing overflow. The use of electronic valves with automatic closing when the water amount is reached is another possibility. It should be possible to avoid foaming through a suitable design of the sprayer tank. It is estimated that water filling might cause from 0 up to 50 g of pesticide spill during the season.

Handling of the concentrated pesticides might cause spraying of droplets during the opening, filling and cleaning of the container. The spill is estimated at 2.5 to 50 g pesticide during the season. Special equipment for filling with concentrated pesticide can reduce spillage as well as water-soluble bags or tablets eliminate spillage. It is recommended that only containers that can be cleaned with the filling equipment should be permitted. Alternatively only returnable containers should be permitted.

Deposition on the outer surfaces of the sprayer and how cleaning the inside and outside of the tank should best be practiced has been investigated in the project.

The result of the deposition study indicates a 0.05 to 0.1% deposition after the spraying of one hectare. This is in complete accordance with other studies. Depending on the concentration in the spray fluid, this means a deposition from 0.5 to 5 g on the outside of the sprayer.

In all events, it is unacceptable to empty the undiluted spray fluid on soil or cleaning sites. The spray fluid should be diluted with water from the rinse tank and sprayed in the field. The dilution and spraying should be repeated 2-3 times until the concentration of the fluid in the sprayers is 1-2% of the initial concentration. Then the residual diluted spray fluid can be emptied through the bottom valve in the field while driving the sprayer. Rinsing instructions are given in the report.

Cleaning is recommended after each day the sprayer has been in use, and it is recommended that rinsing tanks be installed on all sprayers so it is possible to dilute the spray fluid to a concentration of about 1% of the initial concentration. Furthermore, the sprayer should be equipped with high-pressure equipment for cleaning in the field. Parking under a roof or on cleaning sites is recommended.

Spillage should be sorbed with appropriate sorbents and collected for delivery at the municipal receiving stations.

It is recommended that manufacturers of spray equipment develop sprayers with a minimal volume of fluid in the sump and tubings. A typical sprayer contains 10 litres in the sump and 40 litres in the tubings. The volume of the rinse tank has to be 10% of that of the sprayer tank and no less than 150 litres.

Various kinds of cleaning sites are evaluated in the project, and 4 types are recommended: Cleaning site on hard surface with collection of the wastewater in the slurry tank. The pesticide concentration will be 100 to 1,000 times below normal field dose, and it is assessed that the risk of influence on the crop is negligible if concentrated spray fluid is not led to the tank.

Filling and cleaning of the sprayer in the field is recommended if different places are used in the field. It is estimated that up to ten times the normal dose could be reached on a very limited area (10 square metres). It is not expected to give any environmental problems. Transport of the concentrated chemicals must be carried out while taking safety precautions to avoiding accidents, and equipment for collection of any spill has to be brought along in the field.

This report recommends biobeds, especially if cleaning and flushing of the tank is performed in the field. The grass cover should be maintained to secure good evaporation and water balance in the biobed in the spray season to prevent leaching of water-soluble pesticides and metabolites. The depth of the biobed should be at least 50 cm, but with a depth of about 1 metre, the biobed can be used with a high degree of safety with frequent sprayer cleaning on the biobed.

Other solutions are filling and cleaning on hard surfaces with tank collection of wastewater, but the pesticide concentration can reach field dose so precautions should be taken to spray the wastewater on vegetation, which can tolerate the pesticide impact. Cleaning of the wastewater through activated carbon is another possibility, but the carbon filters should be maintained to secure their efficiency.

Cleaning sites with a gravel cover or collection in liquid manure tanks without checks for water tightness must be deprecated. There will be a high risk of pesticide point source pollution if the filling and cleaning of sprayers are carried out at these sites.