Report from the Sub-comittee on the environment and health

Counties analyse samples
<strong>from</strong> sensitive wells for
BAM
18
In <strong>the</strong> case of 2,6-dichlorobenzamide (BAM), which has been detected in
about 14% of <strong>the</strong> screens analysed, <strong>the</strong> data must be treated with caution
because <strong>the</strong> county authorities selected sensitive screens for testing for
this compound. Sensitive screens should be understood to mean screens
in young groundwater near <strong>the</strong> surface or screens close to potential
sources of pollution. BAM is a degradation product, <strong>the</strong> parent
compound of which is dichlobenil. Dichlobenil has not been used for
agricultural purposes and is no longer permitted in Denmark.
The triazine degradation products desethylatrazine, desisopropyl-atrazine
and hydroxyatrazine have been detected in 6.6%, 5% and 2.8%,
respectively. However, hydroxyatrazine has been analysed for in only a
few screens, and experience <strong>from</strong> o<strong>the</strong>r countries does not normally
reveal high detection percentages for this substance.
Table 4.2
Detection of pesticides related to <strong>the</strong> number of analysed screens in <strong>the</strong>
groundwater monitoring programme (GEUS 1998).
Groundwater
monitoring
8 GRUMO
pesticides
Analysed
screens
Detections
above <strong>the</strong>
detection limit
(often 0.01
µg/L)
in
%
Detections above
or equal to <strong>the</strong>
limit value
(0,1 µg/L)
in
%
1014 121 12 35 3.5
Analysis for o<strong>the</strong>r
pesticides than <strong>the</strong>
8 GRUMO
pesticides
594 126 21 76 13
µg/L = microgramme per litre
The extension of <strong>the</strong> monitoring programme in 1998 to approx. 50
pesticides and degradation products may reveal possible fur<strong>the</strong>r
occurrence of pesticides in groundwater, particularly as only a few of <strong>the</strong>
594 screens have been analysed for all 50 substances.
The depth distribution of <strong>the</strong> pesticides shows that <strong>the</strong> eight GRUMO
pesticides occur in 22% of <strong>the</strong> high-lying and youngest groundwater in
<strong>the</strong> interval 0-10 metres below ground level and that <strong>the</strong> frequency
decreases with <strong>the</strong> depth. Where screens have been analysed for more
than eight substances in <strong>the</strong> monitoring programme, pesticides have been
detected in 34% of <strong>the</strong> groundwater samples in <strong>the</strong> interval 0-10 metres
below ground level, see figure 4.2. Of <strong>the</strong>se, 23% of <strong>the</strong> detections were
over or equal to 0.1 microgramme per litre.
It can thus be concluded that pesticides and <strong>the</strong>ir degradation products
occur particularly in young groundwater. This may be due partly to <strong>the</strong>
fact that <strong>the</strong> substances are gradually degraded while being transported
down through <strong>the</strong> aquifers and partly to <strong>the</strong> fact that <strong>the</strong>y are transported
horizontally with <strong>the</strong> groundwater to watercourses, lakes and
groundwater wells. It is also possible that <strong>the</strong> pesticides are transported
towards <strong>the</strong> groundwater so slowly that <strong>the</strong> increased occurrence and
rising concentrations of <strong>the</strong> substances found today in young ground
water will be found in <strong>the</strong> lower aquifers in <strong>the</strong> future. It will only be
possible to assess this when <strong>the</strong>re are longer time series in <strong>the</strong> monitoring