Miljøprojekt, 1163 – Fund af glyphosat og AMPA i drikkevand fra små vandforsyningsanlæg i Storstrøms Amt

Fund af glyphosat og AMPA i drikkevand fra små vandforsyningsanlæg i Storstrøms Amt

Summary

Glyphosate and AMPA were found in 38 out of 193 analyzed small private water plants supplying private households in Storstrøm County in 2001/2002. The water supply systems are all situated in areas dominated by till.

The owners of the 38 plants were contacted, and 28 plants were investigated. Glyphosate and/or AMPA were again found in 2005 in 15 plants, corresponding to 54%. In ten plants glyphosate/AMPA was found in concentrations exceeding 0.1µg/l.

The 15 water plants extracted groundwater near the surface from 14 excavated wells and from 1 drilling situated in an excavated well. Glyphosate/AMPA were not found again in drillings extracting ground water from deeper levels in the reservoirs underbedding till layers.

Twelve water plants were investigated in detail, and the owners were interviewed, e.g. about use of glyphosate on their property: Use of glyphosate was reported close to 6 wells, while glyphosate was not used on the remaining six properties. Eight wells were situated near fields treated with glyphosate, and two wells were situated close to fields treated in the late autumn 2004, but the pesticide was not known.

The main sources of glyphosate/AMPA in the investigated wells were probably ground and surface water from sprayed courtyards and groundwater originating from sprayed fields. However other sources were also reported.

A relation between increasing distance to the source and decreasing glyphosate /AMPA concentrations was found. This means that it is possible to use a distance criterion in relation to wells extracting ground water from reservoirs situated near the surface.

Findings of coli bacteria in manual drillings sampling groundwater near the surface, indicate fast transport from the surface to the uppermost parts (1-2 m below surface) of the ground water in till via macro pore systems. Previous findings of bacteria in wells can therefore also be explained by transport of ground water through pore systems towards the wells.

The 12 localities investigated are situated in areas dominated by till deposited by the Young Baltic Ice during the last glacial advance. The Young Baltic till is also characterized by horizontal fractured zones generated by ice segmentation in Younger Dryas (11,000 BP), where precipitation of ice lenses fractured the clay till sediment. This fissile zone has originally characterized the till from terrain to about 2.5-meter depth, but the depth of the zone will vary locally. The upper boundary of the fissile zone depends on later and recent climatic influence and bioturbation: frost, thaw and desiccation fractures, worm borrows and root channels. Highly porous fissile zones were found at 7-8 localities, where the fissile zones were in direct contact with the wells. It can not be excluded that similar zones can be found at the remaining localities. Several open macro pore systems (root channels, worm burrows or fractures) were found near 7 wells, and near the remaining 5 wells, open worm channels were found.

Multivariable statistic work on analytical data showed two water types with high concentrations of AMPA corresponding to "thin" and "thick" water. Thin water resembles precipitation water quickly transported from the surface towards the upper parts of the ground water in the till or direct to the wells, while "thick" ground water with a larger amount of chloride etc. has a longer residence time in the till reservoirs. A negative correlation between decreasing AMPA concentrations and increasing depth of the water table reflect, that both glyphosate and AMPA concentrations decrease with increasing depth of water sampling. A positive correlation between phosphate and AMPA may reflect high phosphate concentrations in the sediments near the surface, and that AMPA and phosphate presumably follow the same transport patterns.

It is not expected to find a similar vulnerability in sandy areas, unless surface water infiltrates directly towards the wells from sprayed courtyards or other treated areas in the immediate vicinity of the wells.