Transport of Trace Metals by the Rainwater Runoff in the Urban Catchment of Guwahati, India - Management of Natural Resources in a Changing Environment - page 226

Nickel showed a negative correlation with pH values in the runoff locations J, N,
R, U and Z may be due to the leaching of Ni from the soil at lower pH. Most of the
dissolved Ni in surface runoff is likely to occur in complexed form. Moderately
strong metal-complexing ligands in the form of humic substances are responsible
for the complexation of about 20 % of Ni and the remaining Ni is complexed by
ligands with apparent stability constants comparable to those of synthetic chelating
agents (Sedlak et al. 1997 ).
Lead
It occurred in the runoff from 0 to 0.405 mg/L, the highest value being found at the
location, K12. BDL values were recorded by 38 of the samples (42 %).
For the location J, lead could not be detected for the fi rst four events I, II, III and
IV; for the event V there was decreasing trend and for the events VI and VII, no
specifi c trend was observed. For the locations N, K, R and M, Pb was found below
detection level for the fi rst two events while no particular trend in Pb content in the
runoff could be seen for the event III. Also no distinct trend was observed in any
events of the locations U and Z.
The concentration of Pb was in a positive correlation with pH of the correspond-
ing samples. The main source of lead in the atmosphere was tetraethyl lead used
earlier in fuel to improve its octane number. Many soils contain appreciable amount
of Pb from natural sources. Being mostly insoluble, the runoff can remove a small
part of Pb in the soil. In this context, Pb-content of the runoff at some of the loca-
tions can be described as substantial. Long-term exposure to lead or its salts can
affect adversely the nervous system and kidneys (Tebbutt 1983 ; Bloutsos and
Yannopoulos 2011 ).
Zinc
The runoff had zinc from 0.024 to 0.0.408 mg/L with a mean value 0.136. The
sample J7 had the maximum value and M11 and M12 did not show any Zn content.
For the location J, decreasing trend was seen for the three events I, IV and VI,
increasing trend for the three events II, III and V and the rest events did not possess
any distinct trend.
For location N and M, Zn was found in increasing trend for the event I; no gen-
eral trend for the events II and III. In the location K, decreasing trend was seen for
the two events I and II and no specifi c trend for the event III. In the location R, Zn
showed an irregular trend for the event I, decreasing trend for the event II and
increasing trend for the event III. For the location U, the event I showed an increas-
ing diurnal trend while no specifi c trend was seen in II and III events. Location Z
showed no general trend in any of the events.
According to Budai and Clement ( 2011 ), zinc is produced mainly from tyre and
brake wear and the corrosion of galvanized steel. It is likely that the runoff leached
some of Zn in the soil deposited from these sources.