Transport of Trace Metals by the Rainwater Runoff in the Urban Catchment of Guwahati, India - Management of Natural Resources in a Changing Environment - page 224

Co is present in trace amounts naturally in rock, soil, water, plants, animals
and air. Co occupies 0.0025 % of the earth's crust. Co occurs in mineral form as
arsenides, sulfi des and oxides, such as linnaeite (Co 3 S 4 ), carrolite (CuCo 2 S 4 ), saf-
fl orite (CoAs 2 ), skutterudite (CoAs 3 ), erythrite (Co 3 (AsO 4 ) 2 .8H 2 O), and glau-
codot (CoAsS). Co anthropogenic sources are exhaust from vehicles, coal-fi red
power plants and incinerators. Co mining and processing activities, the produc-
tion of alloys and chemicals containing cobalt, sewage effl uents and agricultural
run-off are major anthropogenic contributors of cobalt to the aquatic environ-
ment (Nagpal 2004 ).
In higher concentrations cobalt is toxic to humans and to terrestrial and aquatic
animals and plants. Acute exposure to cobalt may lead to a depression in iodine
uptake, anorexia, nausea, vomiting and diarrhoea (Nagpal 2004 ).
Copper
Its concentration was from below detection level (BDL) to 0.614 mg/L in the runoff.
The sample N9 had the maximum Cu content. 33 of the samples (37 %) had Cu
below detection level.
For location J, Cu was distributed from 0 to 0.446 mg/L with a mean value 0.127.
Cu could not be detected for the events I, II, III, and three samples of the event
IV. Event V had decreasing trend while event VI had increasing trend and for the
event VII, Cu content showed no distinct trend.
In location N, the range of Cu was from 0.022 to 0.614 mg/L with a mean of
0.190. The event I showed decreasing trend while the events II and III showed no
specifi c trend. For location K, Cu content was from 0 to 0.258 mg/L with a mean
0.094. Cu could not be detected in the events I and II. Event III showed no specifi c
diurnal trend. For location M, Cu content was distributed from 0 to 0.283 mg/L with
a mean value 0.121. The behaviour of the events is same as in case of location K.
In location R, Cu was distributed from 0 to 0.019 mg/L with a mean value 0.002.
No Cu could be detected except only two samples from event III. Location U
showed the range of Cu 0.007-0.078 mg/L with a mean value 0.028. No distinct
diurnal variation of Cu could be detected for the events present. Location Z showed
a range of Cu from 0.004 to 0.043 mg/L with a mean value 0.018. Like location U,
here also no specifi c trend could be detected for the two events.
Cu contents of locations J, N, R and Z showed negative correlation with pH as
was also found by He et al. ( 2001 ). This is attributed to the leaching of more Cu
from soil to runoff water in lower pH. Dortwegt and Maughan ( 2001 ) has reported
that Cu at pH <7.0 becomes more stable in solution. This metal has moderate mobil-
ity under slightly acid soil conditions (Zhang et al. 2003 ).
Copper is consistently added to soils in the form of fertilizers, pesticides, live-
stock manures, sewage sludge, and industrial emissions such as vehicle production,
electrical wires, batteries, and electrical apparatus (Li et al. 2009 ). It was found
earlier that Cu concentration in the runoff water from a fi eld was as high as 0.7 mg/L
following long-term application of poultry litter (Edwards et al. 1997 ).