Vulcanization kinetics and reinforcement behaviour of natural rubber-carbon black composites: Addition of Shea-butter versus aromatic oil as plasticizers

This work is a comparative study between Shea butter (SB) and treated distillate aromatic extract oil (TDAE) as plasticizers in the vulcanization of natural rubber (NR)- carbon black (CB) vulcanizates (-CB-S-NR-). The plasticized -CB-S-NR- composites extended scorch (Ts2) and optimum (T90) curing times. The delays in crosslinking reaction were suspected to be due to the increased viscosity (ML) and insulation of the reacting species (NR, CB, Sulfur and other curing aids) by the films of plasticizers. This effect increased the activation energy (Ea (KJ/mol)) for vulcanization. The -CB-S-NR- without plasticizer SB (SBO), showed higher ML, crosslinking density index (ΔM), rheological strength (MH) and low cure reversion properties than others. In comparison, the SB loaded -CB-S-NR- composites showed improvement in ML, ΔM, T90, with lowers Ea (KJ/mol) than TDAE samples. Also, the SB compounds exhibited higher Young's modulus Eo(MPa) than SBO and TDAE compounds. For instance, the Eo(MPa) of SB5 was over 7 and 1200 % higher than SBO and STD5 respectively. However, -CB-S-NR- filled with TDAE generally showed higher strength(MPa), attributed to stronger CB-NR interactions. Therefore, environmentally friendly SB could replace petroleum based oils for compounding rubbers.

Particulate plastics in drinking water and potential human health effects: Current knowledge for management of freshwater plastic materials in Africa

Plastic materials have contributed to the release of environmentally relevant particulate plastics which can be found almost everywhere and may be present in drinking water. Human exposure to these materials is diverse and our understanding of their internalization in the human body is incipient. This review discusses the state of knowledge of particulate plastics exposure in drinking water and the potential risks of adverse health in the human body. Particulate plastics have problematized water systems worldwide, and about 4,000,000 fine plastics may be ingested from drinking water annually by an individual. Testing methods for these materials in environmental media are presently inconsistent and standard protocols do not exist. Their potential ecotoxicological consequences are recognised to be linked to their physicochemical diversity, biological transpositions, and cytological tolerance in living organisms. It is observed that toxicological endpoints are varied and lack properly defined modes of action. In particular, fine particulate plastics have been observed to translocate into body tissues and cells where they are capable of provoking endocrine disruption, genetic mutations, and cancer responses. We propose a reclassification of particulate plastics to cater for their biological deposition and attributable risks of adverse health. Environmental management of particulate plastics in many developing countries is weak and their potential releases into drinking water have received limited research. Given that large populations are exposed to fresh surface water and plastic packaged drinking water worldwide, and that the risk assessment pathways are unvalidated at the moment, we argue for developing countries to increase their capacity for the environmental monitoring and circular management of plastic materials. Large-scale epidemiological cohort studies and surrogate assessment pathways are also recommended to provide a better understanding of the hazard characterization of particulate plastics exposure.

Effect of storage on the levels of phthalates in high-density polyethylene (HDPE) film-packaged drinking water

High-Density Polyethylene (HDPE)-packaged water is a popular choice for urban potable water across Africa. However, the sources and fate of priority chemical contaminants have not been adequately reported. The present study seeks to determine the effect of storage and labelling on the levels of phthalates - dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), benzyl butyl phthalate (BBP) and di(2-hexylethyl) phthalate (DEHP) - in HDPE packaged water. Printed and unprinted 500 mL packet samples, treated water and raw water samples were collected from two major companies in Accra and stored at three temperature levels for 28 days. Phthalates were extracted and pre-concentrated for analysis by GC-MS weekly. The results indicated that phthalates loading became detectable within the first 7 days of incubation, with printed samples showing higher concentrations than unprinted samples at every incubation temperature. The highest concentration was recorded for BBP (1.03 μg/L between a lower and upper confidence limits of 0.62 μg/L and 1.42 μg/L). Temperature significantly affected the concentration of DMP for printed packets (p-value = 0.05) and unprinted samples (p-value = 0.06), BBP across all samples, and DEHP in printed samples (p-value = 0.06). On the other hand, storage duration significantly affected the concentration of BBP across all samples. There was a very strong correlation between printing and the concentration of phthalates in the water samples (p-values <0.001) across the storage temperatures. Effect size analysis established significant differences between site-specific printed and unprinted samples. The present study revealed weak interactions between the selected phthalates and the HDPE matrix, and recommends alternative packaging that can restrict the presence of phthalates and other priority chemicals in plastic packaged drinking water.

Microbial contamination and quantitative microbial risk assessment of high-density polyethylene (HDPE) film sachet drinking water in Ghana

The present research estimated the impact of storage on the microbial quality of high-density polyethylene drinking water. Samples were taken from two popular companies in Greater Accra using a two-sided exact test in SAS JMP to estimate the sample size. The samples were stored across three temperature profiles at 8 °C, 30 °C (average room temperature), and 40 °C (average outdoor temperature) for 28 days. The samples were examined using standard microbiological methods for heterotrophic plate counts (HPCs), faecal coliforms, and Escherichia coli. The data were described and regressed with Microsoft Excel, Argo 4.3.1, and SAS JMP software. The results demonstrated increasing deterioration of the water samples for all microbial indices at all temperatures with increasing storage duration. The highest HPC, faecal coliforms, and E. coli were 1,312; 622; and 252 cfu/100 mL, respectively, all at 40 °C. The daily risk of infection due to E. coli O157:H7 was 5.22 × 10^-5 infections per child per day for children under 5 years, and 1.6 × 10^-4 attacks per adult per day, compared to the upper limit of 1.0 × 10^-6. These results are higher than recommended exposures, and interventions along the sachet drinking water value chain are needed to protect public health.

Evaluation of plastic packaged water quality using health risk indices: A case study of sachet and bottled water in Accra, Ghana

Plastic packaged water is the drinking water of choice for urban populations across Africa but its quality remains questionable in most developing countries. Six hundred (600) packages, consisting of sachet and bottled water, were sampled from two high-end companies in Accra (Ghana) and stored through their shelf lives under an average room temperature of 30 °C. The samples were tested for physicochemical quality and the presence of bacteria and phthalate esters at 2ⁿ × 3 periods, where n is the sampled batch number. The data were described and modelled with embedded Bayesian and Machine Learning algorithms in JASP0.16.0.0 and Argo-4.1.3. The results reported lower than regulated levels of electrical conductivity (163.66 μS/cm), alkalinity (39.67 mg/L), and residual chlorine (<0.01 mg/L) while the pH was generally within specification (6.5-7.7). All samples showed progressive biological contamination following the third week (sachet samples) and the sixth week (bottled water) of incubation. Initial samples, including raw water, processed bulk water and packaged water did not present detectable microbial growth. The total microbial load in sachet samples grew at 0.936 cfu/week and 1.006 cfu/week for the bottled samples although the results did not exceed 1000 cfu/L (0-976 cfu/100 mL). Modelled mean probability of infection was 1.196 × 10^-4 in 67% of the samples. Raw and processed water samples did not show detectable levels of phthalate contaminants. The mean hazard index calculated on the individual hazard quotients of phthalates was 7.41 × 10^-3 ± 8.20 × 10^-4, suggesting lower acute risk potential. Mean integrated lifetime cancer risk (ILCR) was determined to be 1.53 × 10^-3 ± 1.71 × 10^-4 within a range of 2.86 × 10^-4 and 7.18 × 10^-3. Mean child ILCR was about 70% of adult ILCR and increased from 4.16 × 10^-4 to 2.41 × 10^-3 for sachet and 4.93 × 10^-4 to 7.18 × 10^-3 for bottled water. For adult ILCR, sachet water presented 2.86 × 10^-4 to 1.65 × 10^-3, and 3.38 × 10^-4 to 4.93 × 10^-3 for bottled water. This study confirmed the presence of phthalates and pathogenic bacteria in the samples, at-risk levels that require mitigation.