Assessment of Atmospheric Deposition of Heavy Metals Nutrients and Particulate Matter in Air and Soil Around Chiromo Campus

Atmospheric deposition is one of the critical sources of nutrients in the water bodies causing eutrophication. The key nutrients include nitrogen and phosphorous compounds. This has disastrous effects on water bodies which cause eutrophication and consequently affect the aquatic flora and fauna. In addition, deflation of dust contributes to atmospheric concentrations of heavy metals that affect the respiratory system. The major objective of this study was to measure nutrient deposition and to estimate weekly loading of N, P and heavy metals in a manner to understanding their impact on freshwater ecosystems.

Particulate matter  were collected four times on weekly basis using low volume automatic air sampler at Department of Chemistr, University of Nairobi. The samples were collected and analyzed for nitrogen and phosphorous using UV-Vis spectrophotometer. Heavy metals namely lead (Pb), iron (Fe), copper (Cu) and cadmium (Cd) in particulate matter were acid digested and analysed by Atomic Absorption Spectrophotometer. Soil samples from four sites around the campus were collected; the sites were Chiromo hostels, Chiromo library, Department of Chemistry and area around Chiromo River. The samples were acquired using a shovel at least 1 and ½ feet deep and composted. The samples were acid digested and analyzed by AAS.

Heavy metal concentration in dry deposition sample ranged from 3.3-1.88 mg/g (Fe), 0.27-0.13 mg/g (Cd), 0.05-0.01 mg/g (Cu). Lead was below the detection limit in particulate matter.  For soil sample the concentration ranged from 16,900-16,563 mg/kg (Fe), 26.54-22.48 mg/kg (Pb), 4.82-4.63 mg/kg (Cu) and 3.61-2.32 mg/kg (Cd).

The concentration of nitrates in dry deposition sample ranged from 18.61-8-18 mg/g and those of nitrites ranged from 0.33-0.12 mg/g. In soil the concentration was 5,426.58 mg/kg dry weight and the concentration for nitrites was 563 mg/kg dry weight. For phosphates the concentration in dry deposition sample ranged from 0.08-0.04 mg/g particulate and was 1.16-1.10 mg/g soil. The results revealed the presence of heavy metals and nutrients in dry deposition around Chiromo Campus. Further studies should be conducted to cover different seasons and to include more sampling sites.

Key words: Atmospheric deposition, N and P load, Eutrophication, Heavy metals in air 

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