|dc.description.abstract||The concentrations of some heavy metals in soil and plant tissue, resulting from land application of sewage-sludge, were examined by determining the levels of manganese (Mn), iron (Fe), Copper tCu), zinc (Zn) and lead (Pb) in spinach (spinacea oleraceae) and kale (brass ica oleraceae leaves and the total heavy metal content in the soils and sludges used.
The technique used in this analysis was Energy- Dispersive X-ray Fluorescence Spectrometry (EDXRFS). Excitation source used was a radio-isotope 109-cadmium (25 mCi) with a semi-conductor Silicon-lithium Si(Li) drifted detector. The vegetable samples were dried, ground and digested using a mixture of nitric and perchloric acids at a ratio of 3 ;1, Ion precipitation was done by adding a non-selective precipitating agent, sodiumdiethyldithiocarbamate at a pH between 5 and 6 and later filtered through millipore filter membranes.
The samples used were from Nairobi, Nakuru and Kiambu. Those from Nairobi and Nakuru were sampled from farms where sludge from their respective municipalities had been used for many years. Kiambu samples were from farms where farmyard manure had been used to improve the soil quality.
An open air pot experiment was also carried out to investigate whether the uptake of these heavy metals Increases with increase of sludge application.
Sludge and soil were mixed at various percentages (dry weight basis) ranging from pure soil to pure sludge. Vegetables grown in these pots were analysed after maturity.
The general observation was that Nairobi vegetables had high levels of the trace elements compared to the vegetables from other regions.
The metal content in spinach from Nairobi ranged
between the following values. Mn (145 - 1230ugg-1),
Fe (490 -990pgg-1), Cu (16 - 35ngg-1), Zinc (302 - l486ugg_1)
and Pb (7 -l6pgg 1). In kale, the range was Mn (110 - 37l|igg~
Fe(399 - 758ugg_1), Cu (16 - 33ugg_1), Zn (123 - 282ngg-1)
and Pb (6 - llpgg-1).
All samples from Nakuru and Kiambu had lower values than those from Nairobi. In most cases kale had lower trace metal content than spinach from similar environments.
Increase in sludge material (w/w) in both fields had a corresponding increase in manganese copper and zinc content for both vegetables. In field one, increase in levels of Cu( 6.8-25 • 9ngg-l) Zn (152 — 459pgg— 1)
were obtained in spinach while a similar increase in Cu (5.7-10.5 pgg 1), Zn (53 - 142 pgg-1) and Mn (6.4 - 35 pgg *) was obtained for kale.
Lead (Pb) levels in spinach and kale were less than 7 pgg 1 and 5.4 pgg 1 respectively even at the highest level of sludge application in both fields.
In field two, increase of (In (254 - 1119 pgg-1) Cu(15.3 - 31.2 pgg"1) and Zn (137 - 1422 pgg"1) was obtained in spinach.
In kale increase in Pin (8.5 - 276 pgg"1), Cu (3.3 - 14.4 pgg and Zn (47- 536 pgg 1) was obtained.
Pure sludege from Kariobangi had trace average concentrations of elements at the following levels. Mn: 0.21%, Fe: 4.0%, Cu: 208 pgg Zn: 0.18% and Pb: 333 pgg 1.
Nakuru sludge had Pin: 993 pgg-1. pe : 0.38%
Cu: 98 pgg 1, Zn: 0.14% and P b : 8 5.5 ygg~1||