Characterization of polychlorinated biphenyl residues in the North End lake and Port Elizabeth harbour, South Africa

Persistent organic pollutants (POPs), including polychlorinated biphenyls (PCBs) are widespread in aquatic systems, they can bioaccumulate in the tissues of aquatic organisms, especially fish as they occupy a position near the top of the aquatic food web. PCBs are among the most toxic substances and have been shown to cause many adverse effects to humans and wildlife. High health risks are associated with populations that follow a diet high in fat content such as fish and shellfish in which PCBs bioaccumulate. Given the importance of industries and the potential health concerns of exposure to PCBs, the lack of information on environmental levels of PCBs in South Africa (SA) is significant and concerning. Less attention has been directed to analysis of PCBs in the South African environments due to high cost and lack of appropriate equipment. This study was the first conducted in order to assess the levels of PCBs in the environment of Nelson Mandela Bay Municipality (Port Elizabeth). The research was directed at determining the PCB levels in water, sediments, fish and mussels collected in the Nelson Mandela Bay Municipality. The sampling sites, North End Lake (NEL) and Port Elizabeth Harbour (PEH) were selected based on their location and the importance of activities taking place in these areas. In total 456 samples of water (dissolved and particulate phases), sediments, mussels and tissues of fish were analysed. Suitable analytical methods were based on the equipment and materials available at the Nelson Mandela Metropolitan University. Gas chromatography-mass spectrometry (GC/MS) was used to quantify PCBs in the samples using the internal standard method. Six indicator congeners (PCB nos. 28, 52, 101, 138, 153, 180) were chosen because they are mainly present in most PCB mixtures in environmental samples and they are recommended for regular monitoring. These congeners represent about 50% of the total non-dioxin like (NDL) PCBs in food. All these congeners were detected in the samples analysed. The total PCB concentrations in the sediments from the NEL and PEH ranged from 1.60 to 3.06 and from 0.56 to 2.35 ng g-1 dry weight, respectively. The concentrations of total PCBs in Mytilus galloprovincialis ranged from 14.48 to 21.37 ng g-1 wet weight and from 20.84 to 31.34 ng g-1 wet weight in Perna perna. Total PCBs in water ranged from 0.18 to 0.355 ng L-1. The concentrations of total PCBs in the liver, gonads, gills and muscle were 95.69, 57.49, 44.63, 34.14 ng g-1 lipid weight in Cyprinus carpio and 119.73, 59.21, 49.78, 34.63 ng g-1 in Oreochromis mossambicus, respectively. Fish liver was the most contaminated organ due to its high lipid content compared to other parts of fish analysed. The NEL was found to be more contaminated than the PEH. The main potential sources of PCB pollutants in both areas of this study are industrial and municipal discharges. The NEL is surrounded by many industries and serves as a potential pollutant sink due to wastewater and inflow entering into this lake. Four 0.227 kg meals of the edible part of fish (muscle) per month were recommended based on the non-cancer health endpoint and one 0.227 kg meal per month was recommended based on the cancer health endpoint. This research contributed to notify the public and relevant governmental departments on the PCB pollution status of sediments, water and aquatic life in the PEH and NEL

Effect of Practice-Based Learning in Chemistry on Students’ Academic Performance in Rwanda

This study sought to establish the effect of practice-based learning in Chemistry on students’ academic performance in Rwanda. The study used the quasi-experimental research design. The researchers used the pretest-posttest approach whereby prerequisite knowledge of students was tested prior to treatment. Thereafter, the control group was treated in a traditional approach of teaching using lecturing method while the experimental group was trained using the practice-based learning approach. After the teaching period, which took three weeks, students were given a week to prepare for a chemistry achievement test herein referred to as posttest. Results were analyzed and compared to measure the effect of practice-based learning among students in the experimental group. The study established that the experimental group which was taught through the problem-based approach performed better than the control group which was taught through the traditional learning approach. Therefore, practice-based learning significantly improved the performance of the learners. It is recommended that secondary school science teachers should take the advantage of practice-based learning to improve students’ performance in science subjects

Distribution of polychlorinated biphenyl residues in several tissues of fish from the North End Lake, Port Elizabeth, South Africa

The concentrations and distribution of 6 PCB indicator congeners (IUPAC nos. 28, 52, 101, 138, 153, and 180) were measured in 236 organ samples of fish (Cyprinus carpio and Oreochromis mossambicus) from the North End Lake in Port Elizabeth, South Africa. Polychlorinated biphenyls (PCBs) were extracted from the fish muscles, gills, gonads and livers using USEPA method 8082, followed by a clean-up using concentrated sulphuric acid and florisil column chromatography. Analysis was achieved by gas chromatography–mass spectrometry (GC/MS) using the internal standard method. The concentrations of total PCBs in the liver, gonads, gills and muscle were 95.69, 57.49, 44.63, 34.14 ng∙g-1 lipid weight (lw) in C. carpio and 119.73, 59.21, 49.78, 34.63 ng∙g-1 (lw) in O. mossambicus, respectively. These values were relatively low compared to those reported in the literature. PCB levels were predictably highest in the lipid-rich livers. Individual congeners were not distributed homogeneously within the investigated organs. PCBs 153 and 138 were present at higher concentrations than other PCB congeners for both species. PCB contaminants in fish act as indicators of pollution in aquatic ecosystems and are a potential threat to human health when consumed.Keywords: PCBs, tissues, fish, GC/MS, biomagnification, North End Lak

Characterization of polychlorinated biphenyls in surface sediments of the North End Lake, Port Elizabeth, South Africa

The distribution and concentrations of 6 indicator polychlorinated biphenyl (PCB) congeners, nos. 28, 52, 101, 138, 153 and 180, were determined in surface  sediments from the North End Lake in Port Elizabeth, South Africa. Forty-two  surficial sediment samples were collected from different locations covering the  region that receives the majority of the industrial waste, urban effluents and runoff  and thus expected to be contaminated with different degrees of contamination. The analysis was achieved by gas chromatography-mass spectrometry (GC/MS) using  the internal standard method. The total PCB concentrations in the samples ranged from 1.60 to 3.06 ng·g-1 dry weight (dw). The concentrations of congener profiles showed significant differences. Generally, the highest PCB concentrations were  associated with high organic matter contents and small grain size. The highly  chlorinated PCBs dominated with regards to the levels in sediments. PCB 138 was the major contributor to the total PCBs and was detected at 100% of sites. This study provided a snapshot of the PCB contamination status in the North End Lake  sediments, and allowed for a comparison between the investigated system and other systems worldwide.Keywords: PCBs, sediments, organic matter, particle size, North End Lak

Ways School Leaders Support the Teaching of Chemistry

The study aims to reinforce the effective teaching of chemistry in secondary schools through the support of the school leadership in the implementation of the competence-based curriculum (CBC). Interviews were organised and conducted with five headteachers and five deputy headteachers from ten selected schools. The results confirmed that the support provided by the school leadership in teaching chemistry was dominated by 30% of respondents at visiting teachers in classes, provision of some basic teaching materials and encouraging teachers to work in the chemistry department for mutual support and professional growth. However, in some schools, there is a need for prioritising continuous professional development (CPD) opportunities, feedback meetings and analysing school data for decision making. Therefore, this study recommends more efforts in CPDs, avail enough teaching aids and hold the pedagogical review and learning meetings lead by headteachers; analyse and use the school data for continuous improvement and build the school on tangible evidence in positive learning outcomes. Plus more support in engaging learners doing chemistry rather than just giving them chemistry books. Transformational leadership is needed, where all stakeholders share the same vision and mission of the school

Mastering Properties of Organic Compounds through Activity-Based Teaching Technique

Some learners perceive chemistry as a complex subject to learn, saying teaching is boring and not enjoyable. There is a need for making the learning experience more enjoyable to make chemistry easy to understand. This study aims to assess the effect of activity-based teaching techniques compared to the conventional technique on the performance of students in chemistry. The study was quasi-experimental-based research using both pre and post-test, achievement tests. The sample comprised  166 students, as a total number of students in four classes, from a population of 1610 students of the second grade of secondary classes (S2) studying the Properties of Organic Compounds and Uses of Alkanes. Pre-test was conducted, and its data was collected before the intervention, and the post-test was conducted and data was collected after the intervention. Both the descriptive and inferential statistical tests were applied in the analysis. Students’ performance gain in chemistry was higher in the treatment classes as the mean value was 6.81 and the standard deviation was 1.66  (M = 6.81, SD = 1.66) than that of the comparison classes (M = 6.35, SD = 1.78). However, difference was not significant, t(164) = -1.73, p = .085. Teachers should be supported in designing physical pedagogical activities for improving learning outcomes in chemistry

Congener profiles of polychlorinated biphenyls and the effect on marine mussels at an outfall site, Port Elizabeth, South Africa

This study investigated the effect of freshwater as a point source of PCBs contributing to a marine outfall region. Inflowing and outflowing water from the North End Lake, Port Elizabeth, was collected to determine the contamination levels of polychlorinated biphenyls (PCBs). Mussels at the outflow to the sea were also sampled. The samples were analysed by an internal standard method for 6 indicator PCB congeners using gas chromatography/mass spectrometry (GC/MS) in selected ion monitoring (SIM) mode. The total PCB concentrations in the water (dissolved plus particulate phases) ranged from 0.180 to 0.355 ng∙L-1 and from 20.84 to 31.34 ng∙g-1 wet weight (ww) in mussels. Lighter PCB congeners exhibited highest concentrations in the water samples while heavier PCBs were dominant in mussels. PCB-52 was the most abundant in the water samples while PCB-153 was abundant in mussels. To protect human health from the possible effects of eating fish and shellfish contaminated with PCBs, the Environmental Protection Agency regulates that the level of PCBs in water be no greater than 0.17 ng∙L-1 of water. The levels of PCBs in water from the North End Lake were found to be high (0.180 – 0.355 ng∙L-1) compared to the levels recommended by EPA.Keywords: dissolved phase, GC/MS, North End Lake, particulate phase, sedentary organism

A Novel Allele Encoding 7-Hydroxymethyl Chlorophyll a Reductase Confers Bacterial Blight Resistance in Rice

Rice spotted leaf mutants are helpful to investigate programmed cell death (PCD) and defense response pathways in plants. Using a map-based cloning strategy, we characterized novel rice spotted leaf mutation splHM143 that encodes a 7-hydroxymethyl chlorophyll a reductase (OsHCAR). The wild-type (WT) allele could rescue the mutant phenotype, as evidenced by complementation analysis. OsHCAR was constitutively expressed at all rice tissues tested and its expression products localized to chloroplasts. The mutant exhibited PCD and leaf senescence with increased H2O2 (hydrogen peroxide) accumulation, increased of ROS (reactive oxygen species) scavenging enzymes activities and TUNEL (terminal deoxyribonucleotidyl transferase-mediated dUTP nick-end labeling) -positive nuclei, upregulation of PCD related genes, decreased chlorophyll (Chl) contents, downregulation of photosynthesis-related genes, and upregulation of senescence-associated genes. Besides, the mutant exhibited enhanced bacterial blight resistance with significant upregulation of defense response genes. Knockout lines of OsHCAR exhibited spotted leaf phenotype, cell death, leaf senescence, and showed increased resistance to the bacterial pathogen Xanthomonas oryzae pv. oryzae (Xoo) coupled with upregulation of five pathogenesis-related marker genes. The overexpression of OsHCAR resulted in increased susceptibility to Xoo with decreased expression of pathogenesis-related marker genes. Altogether, our findings revealed that OsHCAR is involved in regulating cell death and defense response against bacterial blight pathogen in rice

A case study on chemistry classroom practices in the Rwandan secondary schools

This study aims at assessing the classroom practices of Rwandan chemistry teachers in secondary schools, the second grade (S2), age range between 14 to 16 years old. The classroom observation conducted using the Classroom Observation Protocol for Undergraduate STEM (COPUS). In general, the best practice of group work or collaborative learning and students' engagement was observed. The analysis of the COPUS data reveals that active learning in chemistry classes is dominating, 54% against 42% of passive learning; found high, statistically significant over passive learning at p < .01 (tCritical = 1.89, df = 7, p = .003). The active students' practice is taking 82% of a 2-min time interval across 30 lessons observed, as one class period has 40 min to make 20 intervals of 2 min. Teachers are engaging their students in collaborative learning by assigning them various tasks in groups. These results established the current instructional practices in chemistry classes to draw conclusions and recommendations

Characterization of polychlorinated biphenyls in surface sediments of the North End Lake, Port Elizabeth, South Africa

The distribution and concentrations of 6 indicator polychlorinated biphenyl (PCB) congeners, nos. 28, 52, 101, 138, 153 and 180, were determined in surface sediments from the North End Lake in Port Elizabeth, South Africa. Forty-two surficial sediment samples were collected from different locations covering the region that receives the majority of the industrial waste, urban effluents and runoff and thus expected to be contaminated with different degrees of contamination. The analysis was achieved by gas chromatography-mass spectrometry (GC/MS) using the internal standard method. The total PCB concentrations in the samples ranged from 1.60 to 3.06 ng∙g-1 dry weight (dw). The concentrations of congener profiles showed significant differences. Generally, the highest PCB concentrations were associated with high organic matter contents and small grain size. The highly chlorinated PCBs dominated with regards to the levels in sediments. PCB 138 was the major contributor to the total PCBs and was detected at 100% of sites. This study provided a snapshot of the PCB contamination status in the North End Lake sediments, and allowed for a comparison between the investigated system and other systems worldwide