Trace Metals Concentrations at the Atmosphere Particulate Matters in the Southeast Asian Mega City (Dhaka, Bangladesh)

Atmospheric particulate matters were collected on quartz fibre filters for 24 hours with a low volume sampler from January 2014 to March 2014 at the Southeast Asian mega city (Dhaka, Bangladesh). Particulate matters samples were analysed for eleven trace metals with inductively coupled plasma mass spectrometer (ICP-MS) at Cà Foscari University of Venice, Italy. Trace metals were extracted from filters with digestion method using a mixture of HNO3 and H2O2. The average concentration of the determined trace metals of As, Cd, Ni, Cu, Pb, Cr, Fe, Mn, Zn, Sband Se were 3.06, 6.28, 3.77, 11.98, 305.6, 9.2, 2057.0, 42.2, 303.3, 5.47 and 2.43 ng&#183m&#453, respectively. Arsenic concentration is much lower in the atmosphere of Dhaka, though Bangladesh has severe arsenic problem in the ground water. Lead and cadmium concentrations showed decreasing trend in Dhaka compared than previous measurements—but still they have very high levels compared than Europe and USA. There is very limited information for Mn, Sb and Se concentrations in Dhaka air. Correlation studies showed that several trace metals had potential joint sources of origin, e.g., manganese is highly correlated with iron (r2 = 0.97) and nickel (r2 = 0.84), copper (r2 = 0.86);lead with arsenic (r2 = 0.79) and antimony (r2 = 0.78). Enrichment factors analysis was also done with the data base for the respective metals in earth crust and coal fly ash. As and Cu both have combined sources, whereas Cd, Pb and Zn were from coal fly ash.Trace metals concentrations in Dhaka city air were much higher than Europe and USA but comparable or slightly lower than other south Asian countries. This is the first extensive study for the eleven trace metals with ICP-MS in Dhaka, Bangladesh.

Carbon mineralization in subtropical alluvial arable soils amended with sugarcane bagasse and rice husk biochars

Subtropical recent alluvial soils are low in organic carbon(C).Thus,increasing organic C is a major challenge to sustain soil fertility.Biochar amendment could be an option as biochar is a C-rich pyrolyzed material,which is slowly decomposed in soil.We investigated C mineralization(CO_(2)-C evolution)in two types of soils(recent and old alluvial soils)amended with two feedstocks(sugarcane bagasse and rice husk)(1%,weight/weight),as well as their biochars and aged biochars under a controlled environment(25±2℃)over 85 d.For the recent alluvial soil(charland soil),the highest absolute cumulative CO_(2)-C evolution was observed in the sugarcane bagasse treatment(1140 mg CO_(2)-C kg^(-1)soil)followed by the rice husk treatment(1090 mg CO_(2)-C kg^(-1)soil);the lowest amount(150 mg CO_(2)-C kg^(-1)soil)was observed in the aged rice husk biochar treatment.Similarly,for the old alluvial soil(farmland soil),the highest absolute cumulative CO_(2)-C evolution(1290 mg CO_(2)-C kg^(-1)soil)was observed in the sugarcane bagasse treatment and then in the rice husk treatment(1270 mg CO_(2)-C kg^(-1)soil);the lowest amount(200 mg CO_(2)-C kg^(-1)soil)was in the aged rice husk biochar treatment.Aged sugarcane bagasse and rice husk biochar treatments reduced absolute cumulative CO_(2)-C evolution by 10%and 36%,respectively,compared with unamended recent alluvial soil,and by 10%and 18%,respectively,compared with unamended old alluvial soil.Both absolute and normalized C mineralization were similar between the sugarcane bagasse and rice husk treatments,between the biochar treatments,and between the aged biochar treatments.In both soils,the feedstock treatments resulted in the highest cumulative CO_(2)-C evolution,followed by the biochar treatments and then the aged biochar treatments.The absolute and normalized CO_(2)-C evolution and the mineralization rate constant of the stable C pool(K_(s))were lower in the recent alluvial soil compared with those in the old alluvial soil.The biochars and aged biochars had a negative priming effect in both soils,but the effect was more prominent in the recent alluvial soil.These results would have good implications for improving organic matter content in organic C-poor alluvial soils.