This study was initiated to document information on the levels of sediment contamination with organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs). Moreover, it was intended to identify compounds which impose major ecological risks to aquatic organisms. Surficial sediments were collected from 46 locations within the streams and rivers of the Awash River Basin. In total 30 compounds were included in this study: 16 OCPs, 7 PCBs and 7 PBDEs. The total concentrations of OCPs, PCBs, and PBDEs ranged from 6.63 to 206.13 ng g^-1- dry weight (dw), 0.85 to 26.56 ng g^-1-dw and 3.71 to 18.95 ng g^-1-dw respectively. Out of all the tested OCPs, heptachlor, heptachlor epoxide, p,p′-dichlorodiphenyltrichloroethane (p,p′-DDT) and β-hexachlorocyclohexane (β-HCH) were the most abundant in the study area. The ratio of (β-HCH/∑HCHs) indicated that HCHs were originally from earlier usage of HCH in the area whereas the ratio of (p,p’-DDT/p,p’-DDE) showed that the majority of DDT components were recently introduced into most of the sampling locations. Even though there were relatively low concentrations of PBDEs and PCBs across the sampling sites, substantial amounts of PCBs were observed in Addis Ababa City. According to the established ecological risk indices, p,p’-DDT and γ-HCH are the major concerns for potential adverse ecological impacts. This study provided the first comprehensive information on organohalogenated compounds’ (OCs’) occurrences, spatial distributions, and ecological risks in sediments of the Awash River Basin. Thus, the report will be very useful background information for further studies on sediment contamination with OCs’ in the region. It also adds important first-hand data to the field of fresh water ecology and provides useful empirical evidence for setting pollution control priorities for an ecologically important, yet largely understudied region.

Ticks are known as the vectors of various zoonotic diseases such as Lyme borreliosis and tick-borne encephalitis. Though their occurrences are increasingly reported in some parts of China, our understanding of the pattern and determinants of ticks’ potential distribution over the country remain limited. In this study, we took advantage of the recently compiled spatial dataset of distribution and diversity of ticks in China, analyzed the environmental determinants of ten frequently reported tick species and mapped the spatial distribution of these species over the country using the MaxEnt model. We found that presence of urban fabric, cropland, and forest in a place are key determents of tick occurrence, suggesting ticks were likely inhabited close to where people live. Besides, precipitation in the driest month was found to have a relatively high contribution in mapping tick distribution. The model projected that theses ticks could be widely distributed in the Northwest, Central North, Northeast, and South China. Our results added new evidence on the potential distribution of a variety of major tick species in China and pinpointed areas with a high potential risk of tick bites and tick-borne diseases for raising public health awareness and prevention responses.

Like many areas in developing nations, rapid population growth, a high urbanization rate, and poor waste management practices have been observed in the Awash River Basin. Moreover, no comprehensive study has been conducted in this basin to evaluate sediment contamination with heavy metals. About 46 sampling locations were considered to study heavy metal concentrations, distributions, pollution levels, and potential ecological risks associated with these contaminants. The results indicate that average concentrations of all metals have exceeded their respective background values except Pb and Hg. A comparison with similar studies also revealed that sediments from the Awash River Basin had a high average value for Cd. The mean enrichment values of heavy metals increased in the order of Hg < As < Pb < Ni < Cu < Cr < Zn < Cd. Multivariate analysis revealed that Ni and Cu had common sources. The average potential ecological risk index (ERI = 355.54) indicates high potential toxicity response in the study area. In general, surficial sediment contamination with heavy metals is causing high ecological hazards in Awash River Basin. This study sheds lights on the current level of contamination of heavy metals which are widely distributed across the sediments of rivers and streams of Awash River Basin.