Evaluation of faecal indicators and influence of elevated copper concentrations on indication capacity in tropical source waters of Ndola, Zambia

No consensus has been reached about the applicability of standard and alternative microbial faecalindicators for water quality monitoring in tropical countries. For example, members of the coliformgroup have been doubted as reliable faecal indicators as they have been reported to be of potentialautochthonous occurrence in tropical aquatic habitats. Data from field and experimental studies onfaecal indicator performance are thus urgently needed from different tropical regions throughout theworld in order to reach and develop a more scientifically based monitoring approach. In this study,the microbial water quality of surface and groundwater in a tropical highland city of Ndola, Zambiawas investigated for a period of four months using multiple standard and alternative faecalindicators with the aim of evaluating their applicability and furthermore assess the effect of elevatedcopper concentrations, frequently occurring in this region, on the faecal indication capacity. Thestudy followed a sampling design covering a range of surface and ground water habitats, includingtheir ambient soils, which spanned a range of low to high anthropogenic contamination influence. Inaddition, point faecal sources (raw and treated sewage) and non-point sources (pooled animalfaeces) were investigated. Microbial indicators used in this study were E. coli, faecal coliforms(FC), Total coliforms (TC) and Clostridium perfringens spores (CPS). Chemophysical parameters(temperature, pH, dissolved oxygen, total suspended solids) were included for basic water qualitycharacterisation. E. coli and TC were evaluated using the Chromocult Coliform Agar (CCA), achromogenic agar medium. FC was determined by traditional mFC agar. A fluorogenic medium,Tryptose Sulphite Cycloserine (TSC-P) was applied for CPS enumeration including a pasteurisationstep to select for spores. Selected media were further evaluated by biochemical identification ofrandomly selected colonies using the analytical profile index (API) system. TC revealed the lowestfaecal discrimination potential for the considered surface water habitats. Furthermore, TC could beisolated from all soils investigated, pointing to a ubiquitous occurrence in faecal and non-faecalsources. E. coli and CPS revealed highest discrimination for the considered sampling locations. Inaddition, for surface habitats a high correlation between vegetative E.coli and CP spores wasevident pointing to recent faecal pollution from common faecal contamination sources. The E.colito CPS ratio did not indicate general re-growth activities of E.coli in the investigated aquatic andsoil environments. In one soil habitat (ambient soils from shallow wells) re-growth of E.coli waslikely, pointing to potential non-faecal sources for water habitats in case of active transfer processesbetween those compartments. However, no indications of indicator transfer between soil andaquatic habitats could be found by correlation analysis for the considered study period. A cleardose-response relationship by performed microcosms between the die off rates of E. coli, FC, TCand copper concentrations at human sub-toxic levels (