Environmental Contaminants─Today, Tomorrow, and Forever

A a field, environmental science and engineering has long focused on improving our collective understanding of the processes dictating the formation, transport, and ultimate disposition of environmental contaminants. While the identities of the contaminants of interest continually change, our focus on these fundamental processes remains the same. The five contributions in this issue address a range of pollutants, including both airborne and waterborne. Yeh et al. describe the development of a “Soft Sensor” that relies upon machine learning algorithms to relate input signals acquired by common in-line sensors to water quality parameter outputs that are challenging to measure in the field. In particular, they are interested in using machine learning to predict chemical oxygen demand (COD), total suspended solids (TSS), or Escherichia coli concentrations, based upon inline turbidity, pH, ammonium ion, nitrate ion, and electrical conductivity measurements. The researchers evaluate the potential of this approach using two years of data collected at an onsite wastewater treatment system operating in a South African informal settlement. Encouragingly, their approach was successful at predicting COD (mean absolute percentage error (MAPE) of 14.5%; R2 = 0.96) and TSS (MAPE 24.8%; R2 = 0.99). However, E. coli (MAPE 71.4%; R2 = 0.22) detection remains a challenge and will require extended experimentation and the collection of larger data sets for model parametrization. In their contribution, Zambrana and Boehm reviewed the occurrence of human viruses on fomites (i.e., inanimate objects that may play a role in disease transmission). Using a systemic review based-approach, they surveyed the literature and, based upon the 134 articles that met their search criteria, found that a variety of different virus families have been detected on fomites and that the Coronaviridae are the most commonly reported. They note, however, that this finding most likely reflects expanded interrogation of fomites for SARS-CoV-2 during the COVID-19 pandemic. This contribution highlights the need to expand the range of viral targets examined on fomite surfaces. Such expansion could result in the development of fomite monitoring as a means to quantify the circulation of infectious diseases within a community. As the authors note, however, such a monitoring approach will require additional development of standardized fomite sampling protocols, standardized reporting units, and sample analysis methods that differentiate infectious viruses from noninfectious viral DNA or RNA. James and de Vos et al. examine the environmental impacts of a highly different type of pollution episode. In 2021, an onboard explosion led the M/V X-Press Pearl to catch fire off the coast of Sri Lanka, prior to its ultimate sinking. This fire resulted in the release of hundreds of tons of high-density polyethylene and low density polyethylene resin pellets, or nurdles. Because of the onboard fire, these nurdles were released into the environment in their pristine form as well as in the form of burnt pyroplastics or oil-plastic agglomerates. As part of the nurdle recovery mission, and because of the conditions under which the nurdles burned, the researchers wanted to quantify the levels of polyaromatic hydrocarbons (PAHs) that were associated with them. Astonishingly, the burnt plastic pieces had measured PAH levels as high as 105 ng/g, while the unburnt nurdles had PAH levels in the range of 102−104 ng/g. The extremely high levels of PAHs in the burnt nurdles suggest that they should be considered hazardous waste and should be handled and disposed of appropriately. The need to address atmospheric pollution from CO2 and CH4 is the focus of the remaining two contributions. In their Article, Jones et al. describe a process for the direct air capture of CO2 using amine impregnated porous alumina. They utilized either amine (poly(ethylenimine)) [PEI] or tetraethylenepentamine [TEPA] to remove CO2 from humid air both at 25 °C (terrestrially relevant) and at −20 °C (atmospherically relevant). Of the two amines, TEPA-impregnated alumina performed the best, exhibiting a removal of 1.8 mmol CO2/g of sorbent at 25 °C and 1.6−1.1 mmol/g sorbent at −20 °C. The result suggests that impregnated alumina has potential application as a means to reduce atmospheric CO2 levels. Zhu et al. examine the photocatalytic conversion of methane. On a per-molecule basis, methane is a more problematic greenhouse gas than CO2, and while atmospheric methane levels are considerably lower than atmospheric CO2 levels, they are still sufficiently high that methane is considered the second largest contributor to global warming. Because of this fact, there has been considerable work developing processes to reduce methane emissions. One such approach, and the focus of the Review by Zhu et al., is to utilize photocatalytic oxidation approaches that convert methane into commercially valuable organic chemical products. Such an approach has the potential to convert environmental “waste” into environmental products using solar energy. For such a process to work; however, it is important to carefully design and optimize the photocatalysts. Zhu et al. describe the current state of photocatalyst design and performance. They conclude their Review with a helpful discussion of the key challenges that must be surmounted if