| dc.description.abstract | The extent or leaching of 14C-p,p'-DDT dO\\I1a soil column under laboratory conditions
meta Ions n , CL2I+ , C0-'1,- N-12+ ancI Zn+- on this Ieaching process were
studied using different types of soils. Silty clay soil from Chiromo campus, clay soil Iron
Buruburu (Eastlands, Nairobi) and sandy soil from Kilifi district (Coast province) were used in
the experiment. The soil columns were set up and each was saturated with a solution of a
different metal ion. The pesticide was then injected into the column and the leaching solution
through it over a period of 48 hours after which sections of the columns and the leachates
were analysed for the presence of 14C-p,p'-DDT.
The analyses showed that 14C_p,p'_DDT leached readily down the soil columns even in
the absence of the 'added' metal ions. However, when the metal ions were introduced into the
soil columns, there was a general tendency to increase the extent of leaching, particularly in the
clay soils. This is evident from the fact that of the 0.905 ug/g 14C_p,p'_DDT initially introduced
into the soil columns containing silty clay from Chiromo campus, only 0.134 ug/g was found in
the top most one centimetre section of the blank column (without metal ions). For the column
containing Mn2+ ions, 0.115 ug/g 14C_p,p'_DDT was found in the top 1cm section, 0.082 ug/g
pesticide was found in the top section of the column containing Ni2
+ ions, 0.134 ug/g in the one
containing Cu2
+ ions, 0.129 ug/g in the one containing Zn2
+ and 0.110 pg/g in the one
containing C02
+ ions at the end or the leaching process. The extent of leaching in this soil was
found to be highest in the column containing Ni2
+ ions where up to 0.018 lg/g of the 1,IC_p,p'_
DOT was detected in the bottom 1cm section (depth 17cm) of the column. This was followed
by the column containing Mn ions which had (H)06 lg/g IC-p,p'-DDT in the bottom I cm
section and the one containing Co2
ions which had 0.002 lg/g or the pesticide in the same
section. The pesticide was found only to move up to a depth of 15cm in the columns containing
Zn21 and Cu21 ions in the Chiromo soil.
When clay soil from Buruburu was used, the extent of leaching was again found to be
highest in the column containing Ni2+ ions where 0.006 ug/g of the pesticide was found in the
bottom 1em section. This was followed by the column containing Zn2+ where the pesticide
leached to a depth of about 16cm. In the rest of the columns the J4C-p,p'-DDT leached only to a
depth of about 15cm. The leaching was however found to be faster in the columns containing
Mn2+and Cu2+ions than in the blank column and slower in the column containing C02+ ions.
Leaching was generally found to be less in the clay soil than in the Chiromo silty clay soil.
When the soil was changed to sandy soil (from the coast), much more leaching occurred
than in any of the other two soils. The blank column showed high leaching with a pesticide
concentration of 0.041 ug/g recorded in the bottom lcm section (depth 17cm). The column
containing C02+ions showed even more leaching than the blank, with 0.052 ~g/g J4C-p,p'_DDT
recorded in the bottom lcm section. Leaching in the other columns (containing Mn2+,Ni2+ Cu2+
and Zn2+ ions) was generally lower than in the blank, with the column containing Mn2+ ions
exhibiting more leaching than the others.
From these results it was concluded that the addition of metal ions caused a general
increase in the leaching of oIC_p.p-DDT in the Chiromo and clay soils with the exception of
Co2
which reduces it. Addition of the metal ions to sandy soil caused a general decrease in the
leaching of the pesticide except again of CO2 ions caused all increase ill the leaching. The
extent of leaching also depended Oil the amount of organic 111:1tkrpresent in the soil. The more
the organic matter the less the leaching and vise versa, | en |
