evaluation of commonly used analytic procedures for measuring the concentration
of currently applied pesticides in various environmental compartments, such as in
sediment, or in surface water and groundwater. In developing countries in general,
and in remote and rural regions in particular, the monitoring and exposure assessment of pesticides is often constrained by the remoteness of the area and the lack of
accredited laboratories able to carry out analysis. Time gaps, for example, between
the date of sampling and the date of analysis, are thus unavoidable. The implementation of monitoring programs in mountainous areas consequently calls for a
thorough and critical study of storage conditions and the associated storage
stabilities of the target analyses, particularly during shipment, thus minimizing
the risk of pesticide degradation. In a number of studies, the solid phase extraction
(SPE) technique has been demonstrated to be the method of choice for conserving
pesticides during storage and shipping, and until further analysis can be carried out
(e.g., Ciglasch et al. 2005; Deger et al. 2000; Pichon 2000). Since the required
laboratory devices used for applying SPE are manageable and easy to handle, this
method can be used in almost any remote location. Anyusheva et al. (2011) tested
the long-term stability of several pesticides commonly applied in the mountainous
areas of Vietnam, having been adsorbed by SPE cartridges. The authors compared
the recovery values of pesticides stored for a period of 119 and 319 days under
frozen conditions atÀ18
C. The results indicate that storage time on SPE sorbent
material principally impacts upon pesticide stability; however, the recovery values
of the four pesticides (atrazine, fenitrothion, metalaxyl, chlorpyrifos) measured
after storage for 319 days still exceeded the generally acceptable criteria of 70 %,
indicating that longer storage times can be acceptable at least for selected
pesticides. Nevertheless, the general recommendation is to minimize storage
time, keeping the period between field sampling and analysis as short as possible.
4.4.2 Eco-toxicological Risk Assessment of Pesticide
Concentrations Measured in the Mae Sa River
in Northern Thailand
The mountainous areas of northern Thailand are highly susceptible to the contamination of surface waters due to the application of pesticides in agriculture. Froehlich
et al. (see Chap. 3) showed that <1–11 % of the initially applied pesticide mass
might be lost from the place of application into adjacent surface waters, a loss rate
much higher than in European countries where a rule-of-thumb figure of about
<0.1–1 % has been identified (Flury 1996). The main reasons for the higher rates in
northern Thailand are the steep slopes, high levels and intensity of rainfall and the
presence of well-developed preferential flow pathways.
Due to the toxic nature of pesticides, once they enter surface waters they have to
adversely affect the local aquatic ecosystem. The adverse effect of a pesticide on
the aquatic ecosystem depends mostly on its input rate to the stream or lake and its
4 Agricultural Pesticide Use in Mountainous Areas of Thailand and Vietnam. . .
159
of currently applied pesticides in various environmental compartments, such as in
sediment, or in surface water and groundwater. In developing countries in general,
and in remote and rural regions in particular, the monitoring and exposure assessment of pesticides is often constrained by the remoteness of the area and the lack of
accredited laboratories able to carry out analysis. Time gaps, for example, between
the date of sampling and the date of analysis, are thus unavoidable. The implementation of monitoring programs in mountainous areas consequently calls for a
thorough and critical study of storage conditions and the associated storage
stabilities of the target analyses, particularly during shipment, thus minimizing
the risk of pesticide degradation. In a number of studies, the solid phase extraction
(SPE) technique has been demonstrated to be the method of choice for conserving
pesticides during storage and shipping, and until further analysis can be carried out
(e.g., Ciglasch et al. 2005; Deger et al. 2000; Pichon 2000). Since the required
laboratory devices used for applying SPE are manageable and easy to handle, this
method can be used in almost any remote location. Anyusheva et al. (2011) tested
the long-term stability of several pesticides commonly applied in the mountainous
areas of Vietnam, having been adsorbed by SPE cartridges. The authors compared
the recovery values of pesticides stored for a period of 119 and 319 days under
frozen conditions atÀ18
C. The results indicate that storage time on SPE sorbent
material principally impacts upon pesticide stability; however, the recovery values
of the four pesticides (atrazine, fenitrothion, metalaxyl, chlorpyrifos) measured
after storage for 319 days still exceeded the generally acceptable criteria of 70 %,
indicating that longer storage times can be acceptable at least for selected
pesticides. Nevertheless, the general recommendation is to minimize storage
time, keeping the period between field sampling and analysis as short as possible.
4.4.2 Eco-toxicological Risk Assessment of Pesticide
Concentrations Measured in the Mae Sa River
in Northern Thailand
The mountainous areas of northern Thailand are highly susceptible to the contamination of surface waters due to the application of pesticides in agriculture. Froehlich
et al. (see Chap. 3) showed that <1–11 % of the initially applied pesticide mass
might be lost from the place of application into adjacent surface waters, a loss rate
much higher than in European countries where a rule-of-thumb figure of about
<0.1–1 % has been identified (Flury 1996). The main reasons for the higher rates in
northern Thailand are the steep slopes, high levels and intensity of rainfall and the
presence of well-developed preferential flow pathways.
Due to the toxic nature of pesticides, once they enter surface waters they have to
adversely affect the local aquatic ecosystem. The adverse effect of a pesticide on
the aquatic ecosystem depends mostly on its input rate to the stream or lake and its
4 Agricultural Pesticide Use in Mountainous Areas of Thailand and Vietnam. . .
159