Pesticide Residues in Vegetation - Pesticides: Evaluation of Environmental Pollution - page 310

Kisimba (2007) in Tanzania and by Barriada-Pereira et al. (2005) in Spain (values not
shown, outliers). It can be said that the temporal evolution of DDT continues the pattern
of applications, which agrees with the ideas published by Stemmler and Lammel (2009).
The relationship between p,p'-DDE and p,p'-DDT may be an indicator of the age of
DDT in the environment, since the p,p'-DDE is a breakdown product (Rapport and
Eisenreich 1986). Figure 10.4b shows a general increase in this ratio, indicating that
DDT sources have decreased along the years; but there are still sources of emission of
these organochlorine compounds in some areas, as Wang et al. (2007) and Stemmler
and Lammel (2009) indicated, in India and many Asian and African countries, where
dicofol is used as a miticide, a product that contains a high concentration of p,p'-DDT
and o,p'-DDT.
HCH concentrations in vegetation samples have been studied during the period between
1991 and 2006. Throughout this period, there has been a reduction in the presence of
α-HCH congeners and γ-HCH (the most studied) in vegetation. The highest concentrations
were recorded in 1991 and 1994 (Figure 10.5a). In 2005 and 2010, high concentration levels
of HCH were found in contaminated areas of Tanzania (Mahugija-Marco and Kisimba
2007) and Spain (Barriada-Pereira et al. 2005), which have not been included in the studies
of temporal evolution, because they were considered outliers.
According to Atlas and Giam (1988), the proportion of these isomers (α-/γ-HCH ratio)
is an indicator of the age of lindane in air, so that the higher the ratio, the higher is the
seniority. The relationship between the concentrations of both the isomers in plant sam-
ples throughout the years (Figure 10.5b) has been studied, and there has been a substantial
reduction from 1991 to 1994 and then an increase such that in 2003, the values obtained
were around 1.5/1. The results suggest the widespread use of γ-HCH in the middle of the
1990s and then a gradual decrease since its use was banned in many countries, although
it is still used in some areas as Wang et al. (2007) noted after detecting high levels of HCH
in the Himalayas.

α -HCH
γ -HCH

60

40

20

0

1990 1993 1996 1999 2002 2005

(a)

3,5

3

2,5

2

1,5

1

0,5

0

1991 1992 1994 2001 2003

(b)

FIGURE 10.5
(a) Temporal evolution of concentrations of α-HCH y γ-HCH in vegetation samples from 35 countries around the
world. (b) Temporal evolution of α-HCH / γ-HCH ratio.