Heavy metal content in Amaranthus Hybridus, Bidens Pilosa and Pennisetum as environmetal pollution indicators in Nairobi city
One of the effects of the on going urbanization and industrialization is the accumulation of heavy metals in the environment. The influx of second hand vehicles and failure of rain in recent years has lead to increase in the use of leaded fuel in Kenya. This has lead to increased levels of heavy metals in the environment especially in the city of Nairobi. The exposure of man to these heavy metals has caused global concern due to their effect on human health and because of this, there is need to continue monitoring heavy metal levels in the environment and to develop ways of reducing them. The present study determined the levels of Pb, Cu and Zn in Amaranthus hybridus, Bedens pilosa, Pennisetum purreum and soils in the city of Nairobi as an indicator of the extent of heavy metal pollution. The samples were randomly collected in the city and its environs. The concentrations of heavy metals was determined using AAS. The lead content in amaranthus hybridus ranged from 6.8 ± 422g/g with a mean of 81.78±85.98g/g. The lead content in the soil from where it was sampled had a range of 6.6 - 395.1ug/g with a mean of 128.5 133.98g/g. Bidens pilosa had lead content in the range of 8.2 - 354g/g with a mean of 83.1115.52g/g and the soil from where it was sampled had a range of 20.8 - 508g/g. Pennisetum purreum had Pb content in the range of 13.0 - 426g/g with a mean of 89.95145.11g/g and the soil from where it was sampled had a range of 14.4-634g/g with a mean of 144.7 ± 203.15g/g. Amaranthus hybridus had zinc content in the range of 36.6 - 270g/g with a mean of 161 96.17g/g. Bidens pilosa had zinc content in the range 22.9 - 251.8g/g with a mean of 137.683.53g/g. The soil where it was sampled had a range of 20.6 - 395.0g/g with a mean of 169.68 91.10g/g. Pennisetum purreum had zinc content in the range of 38.2- 155.4g/g with a mean of 85.2025.15g/g and the soil where these samples were collected was in the range of 54.4 - 369.5 with a mean of 144.789..1g/g. The Amaranthus hybridus had a copper content in range of 5 - 51.2g/g with a mean of 17.5±12.71g/g and the soil where these samples were collected from had a range of 6 - 238.8g/g with a mean of 43.8 ± 055.54g/g. Bidens pilosa had copper in the range of 2.2 - 84.4g/g with a mean of 22.3 ±19.72g/g and the soil from where these samples were collected had a range of 3.4 - 238.8g/g with a mean of 37.8 = 57.92g/g. Pennisetum perreum had copper in the range of 0.4 - 74g/g with a mean of 24.3 = 25.15g/g. The soil where these samples where collected had a range of 7.8 - 230.6g.g with a mean of 33.2 = 58.16g/g. Most samples had higher levels of Pb as compared to baseline levels of (0.1 - 20g/g) of unpolluted environment. It was also found that the Pb concentration decreased rapidly as the distance from a busy road increased. The city center and industrial areas had higher Pb levels than other areas. Samples from areas with heavy, slow moving vehicles such as round-abouts, corners, bus stops, pot-holed roads, valleys and uphills had higher Pb levels than other areas. This may indicate that the Pb pollution may be from the leaded petrol used in motor vehicles. It was also noted that the washing of amaranthus hybidus removed some of the adsorbed Pb but still the percentage left (46 - 95%) was higher than the baseline levels (0.1 - 20g/g). Therefore the results indicate that Nairobi city had high levels of heavy metals. The amaranthus and the blackjack showed the same trend in the concentration of these metals hence can be used as biomonitors.