Linking Macroinvertebrates and Physicochemical Parameters for Water Quality Assessment in the Lower Basin of the Volta River in Ghana.

The health of the lower basin of the Volta River in Ghana was evaluated in January-February and May-June 2016 using physicochemical parameters and benthic macroinvertebrates sampled at 10 locations. Selected environmental variables were compared to accepted environmental water quality standard values where applicable. Principal component analysis (PCA) and redundancy analysis (RDA) were used to analyse the association between the benthic macroinvertebrates distribution and physicochemical variables. Pesticide concentrations were generally below the limit of detection 0.01 and 0.005 µg/L for organophosphate/synthetic pyrethroid and organochlorines respectively. Nutrient levels were also generally low; however, significant differences existed between the values of physicochemical parameters at the different sampling sites and seasons (Monte Carlo permutation test; p = 0.002), as well as between the abundance of macroinvertebrates at the different sites and seasons (p = 0.002). The environmental variables dissolved oxygen (DO), phosphate, pH, substratum (p < 0.05), turbidity, conductivity, total dissolved solids, total solids and nitrate (0.05 < p < 0.10) significantly explained the variation in macroinvertebrate composition between sampling stations in the Volta River. Polypedilum fuscipenne, was positively correlated with turbidity and DO concentrations; Physa sp., Centroptilum sp., Centroptiloides sp., Phaon iridipennis and juvenile fish were positively correlated with nitrate concentration and pH and negatively correlated with turbidity and DO. Polluted sites were dominated by the snail Lymnaea glabra. This demonstrates that physicochemical parameters and macroinvertebrates could be applied to describe the water quality and improve the biomonitoring for water resources management and the environmental protection in the Lower Volta River.

Environmental risk assessment of pesticides currently applied in Ghana.

Registration of pesticides for use in Ghana is based on prospective environmental risk assessment (ERA) to assess the risks of future pesticide use on the environment. The present study evaluated whether pesticides currently used by Ghanaian farmers may harm the aquatic and terrestrial environment under day-to-day farm practice by performing a 1st tier ERA for terrestrial and aquatic environment and a 2nd tier ERA for the aquatic environment using existing scenarios and models. Results of the 1st tier risk assessment indicated that in the investigated regions in south Ghana, many pesticides might pose an acute risk to aquatic ecosystems adjacent to the treated fields while lambda cyhalothrin, chlorpyrifos, cypermethrin, dimethoate, mancozeb, carbendazim, sulphur, maneb and copper hydroxide may pose the highest chronic risks. Butachlor, dimethoate and carbendazim may pose acute risks to the terrestrial soil ecosystem, while glyphosate, chlorpyrifos, imidacloprid, dimethoate, mancozeb, carbendazim, maneb, copper hydroxide and cuprous oxide may pose the highest chronic risks. Many insecticides and some fungicides may pose acute risks to bees and terrestrial non-target arthropods. The 2nd tier acute aquatic risk assessment showed that most risks were substantiated using species sensitivity distribution (SSD). Actual pesticide use was a factor of 1.3-13 times higher than the recommended label instructions, indicating a general practice of overdosing. The case study shows that the PRIMET model in combination with the SSD concept may offer pesticide registration authorities in Ghana a means to assess environmental risks associated with pesticide usage in a user-friendly and cost-effective manner.

Pesticides Decrease Bacterial Diversity and Abundance of Irrigated Rice Fields.

Bacteria play an important role in soil ecosystems and their activities are crucial in nutrient composition and recycling. Pesticides are extensively used in agriculture to control pests and improve yield. However, increased use of pesticides on agricultural lands results in soil contamination, which could have adverse effect on its bacterial communities. Here, we investigated the effect of pesticides commonly used on irrigated rice fields on bacterial abundance and diversity. Irrigated soil samples collected from unexposed, pesticide-exposed, and residual exposure areas were cultured under aerobic and anaerobic conditions. DNA was extracted and analysed by 16S rRNA sequencing. The results showed overall decrease in bacterial abundance and diversity in areas exposed to pesticides. Operational taxonomic units of the genera Enterobacter, Aeromonas, Comamonas, Stenotrophomonas, Bordetella, and Staphylococcus decreased in areas exposed to pesticides. Conversely, Domibacillus, Acinetobacter, Pseudomonas, and Bacillus increased in abundance in pesticide-exposed areas. Simpson and Shannon diversity indices and canonical correspondence analysis demonstrated a decrease in bacterial diversity and composition in areas exposed to pesticides. These results suggest bacteria genera unaffected by pesticides that could be further evaluated to identify species for bioremediation. Moreover, there is a need for alternative ways of improving agricultural productivity and to educate farmers to adopt innovative integrated pest management strategies to reduce deleterious impacts of pesticides on soil ecosystems.