Assessment of heavy metal status and identification of source in soils under intensive vegetable growing areas of Brahmaputra valley, North East India

This study investigated the content of Cd, Pb, Cr, and Ni in the soils of intensive vegetable growing areas of the Brahmaputra valley, North East India, to assess their status and detect any buildup of metals due to long-term and continuous application of agrochemicals and organic manures. The content of heavy metals was determined in eighty composite surface soil samples (0-20 cm) collected from eight different locations of the valley having a history of more than forty years of vegetable production. This finding is novel as no comprehensive investigation has been done till date in respect of the content of heavy metals in the intensive vegetable growing areas of Brahmaputra valley. The locations are considered free from any pollution caused by industrial effluent or urbanization processes. The investigational data showed that the content of Cd, Pb, Cr, and Ni in the soils ranged from 0.43 to 3.24, 6.00 to 22.90, 3.00 to 15.24, and 3.30 to 14.30 mg kg^-1, respectively. The overall mean values of the heavy metals showed a decreasing order of Pb (14.79 mg kg^-1) > Cr (8.87 mg kg^-1) > Ni (8.37 mg kg^-1) > Cd (1.43 mg kg^-1). The findings of the study indicated significant enrichment of the metals in the surface soils over the local background values of the elements measured in the C horizon. Though the concentrations of Pb, Cr, and Ni of the soils were well below the reference levels used in different countries, Cd showed distinctly higher value with maximum enrichment level. The soils were categorized as slightly to moderately polluted based on different pollution indices. Based on the ecological risk index, soils were in the low-risk category, but in respect of Cd, most of the soils fell under the moderately risky category. Multivariate analysis suggested the predominance of lithogenic influence on the content of Pb, Ni, and Cr while Cd content bears a distinct signature of the anthropogenic source. The buildup of Cd in the studied soils is a matter of critical concern and needs proper monitoring and management strategies to avoid any potential detrimental effect on soil, crop, and human health.

Vermiremediation of toxic jute mill waste employing Metaphire posthuma

India has a giant jute-producing basket which produces considerable quantity of toxic jute mill waste (JMW). Conversely, report on usability potential of JMW is rather scanty. The present study illustrates the efficiency of vermicomposting in bioconversion of JMW for agricultural use. Various combinations of JMW, cow dung, and vegetable waste were fed to Metaphire posthuma in vermireactors. Rapid increment of earthworm count, body weight, and cocoon production was evidenced. Total organic carbon and pH reduction was noteworthy, but N, P, and K availability, formation of stable humic acid C, fulvic acid C, and microbial biomass C substantially increased due to vermicomposting. FTIR spectroscopy confirmed a higher stability of vermicomposted JMW over the composted product. A significant decline in heavy metal concentration (Cr, Pb, Fe, and Zn) in the vermicomposted JMW further establishes the potential of vermicomposting with M. posthuma in successful conversion of the toxic JMW into valuable product.

Spatiality, seasonality and ecological risks of heavy metals in the vicinity of a degenerate municipal central dumpsite in Enugu, Nigeria

BACKGROUND

Improper waste disposal is responsible for the contamination of both surface and ground water resources. Heavy metals leached from improperly disposed solid waste constitute grave environmental and health hazards because of their toxic and persistent nature. There are thousands of open dumps in Nigeria one of which is the Enugu State Waste Management Authority dumpsite.

METHOD

Forty sampling nodes were systematically established around the Enugu State waste Management Authority central dumpsite located at Ugwuaji, Enugu State, Nigeria. Ten heavy metals (arsenic, cadmium, cobalt, copper, chromium, iron, lead, manganese, nickel and zinc) were sampled at different depths of each node in both rainy and dry seasons.

RESULT

Iron and lead were the predominant metals in the vicinity of the waste dump with average values of 132.10 mg/kg and 117.52 mg/kg respectively. The order of abundance of the ten heavy metals monitored is Pb > Fe > As > Zn > Cu > Co > Ni > Cd > Cr > Mn. Generally, there was significant correlation (0.25 to 0.74) among all the metals except between cobalt and manganese in the rainy season. In the dry season, all the metals were significantly correlated (0.29 to 0.813) except for copper and lead, copper and arsenic, zinc and arsenic, and cobalt and manganese. The concentrations of most of the heavy metals approached a constant level at a depth of 1 m. On the other hand, the concentrations of arsenic, cobalt and iron continued to decrease even at a depth of 2 m. The pollution loading index values for the soil are 1.706 for rainy season and 2.54 for dry season.

CONCLUSION

The high pollution loading index represents a significant level of deterioration. It can be concluded that the dumpsite constitute a serious environmental and health hazard.