Relating SARS-CoV-2 shedding rate in wastewater to daily positive tests data: A consistent model based approach

During the COVID-19 pandemic, wastewater-based epidemiology (WBE) has been engaged to complement medical surveillance and in some cases to also act as an early diagnosis indicator of viral spreading in the community. Most efforts worldwide by the scientific community and commercial companies focus on the formulation of protocols for SARS-CoV-2 analysis in wastewater and approaches addressing the quantitative relationship between WBE and medical surveillance are lacking. In the present study, a mathematical model is developed which uses as input the number of daily positive medical tests together with the highly non-linear shedding rate curve of individuals to estimate the evolution of global virus shedding rate in wastewater along calendar days. A comprehensive parametric study by the model using as input actual medical surveillance and WBE data for the city of Thessaloniki (~700,000 inhabitants, North Greece) during the outbreak of November 2020 reveals the conditions under which WBE can be used as an early warning tool for predicting pandemic outbreaks. It is shown that early warning capacity is different along the days of an outbreak and depends strongly on the number of days apart between the day of maximum shedding rate of infected individuals in their disease cycle and the day of their medical testing. The present data indicate for Thessaloniki an average early warning capacity of around 2 days. Moreover, the data imply that there exists a proportion between unreported cases (asymptomatic persons with mild symptoms that do not seek medical advice) and reported cases. The proportion increases with the number of reported cases. The early detection capacity of WBE improves substantially in the presence of an increasing number of unreported cases. For Thessaloniki at the peak of the pandemic in mid-November 2020, the number of unreported cases reached a maximum around 4 times the number of reported cases.

A physicochemical model for rationalizing SARS-CoV-2 concentration in sewage. Case study: The city of Thessaloniki in Greece

Detection of SARS-CoV-2 in sewage has been employed by several researchers as an alternative early warning indicator of virus spreading in communities, covering both symptomatic and asymptomatic cases. A factor that can seriously mislead the quantitative measurement of viral copies in sewage is the adsorption of virus fragments onto the highly porous solids suspended in wastewater, making them inaccessible. This depends not only on the available amount of suspended solids, but also on the amount of other dissolved chemicals which may influence the capacity of adsorption. On this account, the present work develops a mathematical framework, at various degrees of spatial complexity, of a physicochemical model that rationalizes the quantitative measurements of total virus fragments in sewage as regards the adsorption of virus onto suspended solids and the effect of dissolved chemicals on it. The city of Thessaloniki in Greece is employed as a convenient case study to determine the values of model variables. The present data indicate the ratio of the specific absorption (UV₂₅₄/DOC) over the dissolved oxygen (DO) as the parameter with the highest correlation with viral copies. This implies a strong effect on viral inaccessibility in sewage caused (i) by the presence of humic-like substances and (ii) by virus decay due to oxidation and metabolic activity of bacteria. The present results suggest days where many fold corrections in the measurement of viral copies should be applied. As a result, although the detected RNA load in June 2020 is similar to that in April 2020, virus shedding in the city is about 5 times lower in June than in April, in line with the very low SARS-CoV-2 incidence and hospital admissions for COVID-19 in Thessaloniki in June.

Evaluation of interactions between soil and coal fly ash leachates using column percolation tests

The aim of this work was the assessment of the environmental impact of different origin fly ashes with regard to their final disposal. The experimental procedure included the performance of single column tests and column tests of fly ash and soil in series. The appraisal of the potential environmental hazards was implemented using physicochemical analyses and bioassays. Two different fly ash samples were examined, one fly ash produced from the combustion of sub-bituminous coal (CFA) and one fly ash produced from the combustion of lignite (LFA). Single column percolation tests were performed according to NEN 7343 protocol, while fly ash/soil experiments were conducted incorporating slight modifications to this protocol. The study focused on the release of metals Ba, Cr, Cu, Mo, Se and Zn and the ecotoxic behavior of leachates on crustacean Daphnia magna and bacteria Vibrio fischeri. The infiltration of the leachates of both fly ashes through soil affected considerably their leaching profile. The transport of Cu and Zn was facilitated by the dynamic leaching conditions and influenced by the pH of the leachates. Moreover, the release and bioavailability of Cr, Cu and Zn was probably altered during the infiltration experiments and organisms' response was not always correlated with the concentration of metals. Nevertheless, the results are signalling that possible manipulations and final disposal of fly ash should be considered when environmental threats are investigated.

Environmental hazard assessment of coal fly ashes using leaching and ecotoxicity tests

The environmental hazard of six coal fly ash samples collected from various coal incineration plants were examined in the present study, using various leaching tests along with physicochemical and ecotoxicological analyses. Physicochemical analyses indicated that the concentration of Ba, Cr, Mo, Se, sulfates and total dissolved solids (TDS) exceeded the threshold values, according to the European Council decision 2003/33/EC for inert, non-hazardous or hazardous waste. The highest sensitivity, among examined organisms, was presented by Daphnia magna and was ascribed to the lowest tolerance of the organism to Cr. The toxic effect profile of the leachates toward Vibrio fischeri revealed that its bioluminescence was significantly altered by the presence of heavy metals in the leachates (such as Cu, Ni and Zn) in low or sub-lethal doses. Although the toxicity of the leachates toward Pseudokirchneriella subcapitata was relatively high, the correlation between the toxicity and heavy metals concentration was rather poor, indicating the significance of the bioavailability of constituents and the importance of toxicity testing. Based on the classification of the samples resulted by physicochemical analyses of the leachates and the results of ecotoxicity tests, Physicochemical and Ecotoxicological indices were also defined, for an overall evaluation of the environmental impact assessment of fly ashes. The suggested indices showed that ecotoxicity tests were in some cases inconsistent with the outcome of waste classification based on physicochemical analyses. Moreover, the examination of leaching protocols and obtained results showed that one stage leaching test (L/S=10 L/kg) underestimated the fly ash classification, when compared with the two stage test EN 12457-3 at the cumulative ratio L/S=10 L/kg. In addition, the application of availability test NEN 7341 provided useful results about the ecotoxicity wastes. Thus, NEN 7341 is strongly suggested for the implementation of such studies, since the bioavailability of constituents may not be altered by pH adjustment tactics and pH-originated toxicity effects may be avoided.

Toxicological and ecotoxic impact of secondary and tertiary treated sewage effluents

Secondary sewage effluents are discharged in significant quantities in aquatic environments delivering pollutants that were not removed during treatment; yet advanced treated effluents are not lacking of contaminants. In this study, biochemical biomarkers were measured in liver and kidney of rainbow trout (Oncorynchus mykiss) exposed to unchlorinated, chlorinated and tertiary treated secondary sewage effluents. In addition, organic matter, nitrogen and suspended solids were assayed, while a common bioassay, Daphnia magna 21d reproduction test was also applied in order to examine potential relation between the performed bioassay and the biomarkers. Processes using oxidative conditions, such as ozonation and chlorination, resulted in significantly increased breeding rate (up to 74%) of the organism. Biomarkers measurements incorporated the determination of total glutathione (GSH), glutathione S-transferases (GST), glutathione peroxidase (GPX), lipid peroxidation (LPO) and an innovative biomarker in such applications, haem peroxidase. In general, the response of biomarkers was dependent upon the treatment method and it was tissue specific. Secondary effluents inhibited liver GST and haem peroxidase, while GSH levels and LPO were significantly provoked in liver. Ozonation provoked hepatic peroxidation, in terms of haem peroxidase and LPO, and GST; while the protective (to Reactive Oxidant Species - ROS) GSH was depleted, suggesting extended ROS attack to the organism. Similar response of biomarkers (but to a lesser extend) was observed after exposure of trout to effluents submitted to both coagulation and ozonation, emphasizing the significance of removing the residual organic matter by other methods than oxidative ones. Ozonation also enhanced renal LPO and GPX; however the former employment of coagulation limited the peroxidation phenomena. Chlorination mainly affected the levels of total GSH in both tissues.

Influence of ozonation on the in vitro mutagenic and toxic potential of secondary effluents

Reclamation of municipal effluents by advanced treatment processes is an attractive perspective for facing certain water shortage problems. However, the application of tertiary techniques should be thoroughly examined for their potential hazardous effects. Ozonation is an efficient chemical oxidation method, often used in wastewater reclamation, which may result in by-products that may alter the toxic and mutagenic properties of effluents. In this study, Ames test and Microtox test were used for the evaluation of ozonation efficiency to upgrade secondary effluents quality. In general, the toxic response and mutagenic effect without metabolic activation of test species were influenced mainly by the ozone dose and ozonation duration, whereas the mutagenic effect with metabolic activation was influenced mainly by ozone dose, indicating that ozone conditions strongly affect the formation of by-products. In most cases, the toxicity was increased and reached up to 100% (in relation to that of secondary effluent) after ozonation with 8.0 mg O3/L for 5 min. On the contrary, in most cases the mutagenic activity towards strain TA98 without metabolic activation was reduced, when ozone dose and contact time increased. However, the mutagenicity was also increased after ozonation at low ozone doses and for contact times less than 5 min. The mutagenic activity of treated effluents towards strain TA98 with metabolic activation remained about the same or was reduced, compared to that of secondary effluent, and was even eliminated after ozonation with 8.0 mg O3/L for contact times higher than 5 min.

The effect of coagulation on the toxicity and mutagenicity of reclaimed municipal effluents

The objectives of this work were the assessment of the effectiveness of coagulation on the reclamation of secondary effluents and the evaluation of the quality of reclaimed waters by the examination of their ecotoxic and mutagenic properties. Aluminum coagulants resulted in higher removal of organic content, than iron coagulant, reaching up to 40%; the removal of heavy metals, such as zinc and copper was enhanced by the addition of a low strength anionic flocculant. The toxicity of pre-concentrated samples to the bacteria Vibrio fischerii was related to the heavy metal content, especially zinc and copper, indicating the significance of the metals bioavailability and their potential interactive effects. The secondary effluents exhibited mutagenic effects on strain TA 98; these effects were increased during coagulation with ferric chloride (both in absence and presence of flocculant). However, the addition of aluminum coagulants resulted in a decrease of mutagenic potential of secondary effluents, due to the extended removal of organic matter.

Ecotoxicological properties of wastewater treated using tertiary methods

The objective of this work was the examination of the efficiency of coagulation and ozonation processes for the production of reclaimed wastewater with low toxicity. Municipal secondary effluents were treated by FeCl3, Al2(SO4)3 (alum), and a commercial substance at metal ion concentrations of 0.5 and 1 mmol/L. Alternatively, the effluents were treated by ozonation in a semibatch ozone reactor. The feed gas was introduced at a flowrate of 3 L/min containing ozone at various concentrations, ranging between 2.5 and 8 mg/L; ozone residence times were 2, 5, 15, and 30 min. The toxic effects of the advanced treated effluents were examined by a battery of tests using the marine bacteria Vibrio fischeri, the freshwater crustaceans Daphnia magna, Daphnia pulex, and Thamnocephalus platyurus, and the rotifers Brachionus calyciflorus. The addition of alum decreased the toxic effect of reclaimed wastewater on immobilization of D. pulex, from 90 to 60%. Ozonation was also effective for toxicity removal, which decreased to 25% effect on D. pulex after treatment by 2.5 mg O3/L for 2 min. However, acute toxic effects after ozonation, were observed on V. fischeri and were related to ozone gas concentration and contact time. At the highest ozone dosage, the toxicity reached almost 100% inhibition of bioluminescence after 15 min. The toxicity of the ozonated effluents to bacteria decreased with sample storage time and was almost negligible after 48 h, indicating that the potential adverse effect of reclaimed wastewaters on receiving waters might be reduced by storage for a certain time.

Interactive toxic effects of heavy metals and humic acids on Vibrio fischeri

The effect of humic acids (HAs) on the toxicity of copper, zinc, and lead was investigated using the photobacterium Vibrio fischeri (Microtox test) as a test organism. The effects of HAs on metal toxicity were evaluated as functions of time and concentration in pure compound solutions. The toxicities of copper and lead were generally comparable, while the toxicity of zinc was lower than those of the other two metals. The toxicity of copper decreased with the addition of HAs, while the toxicity of zinc remained almost constant. On the other hand, the toxicity of lead increased, depending on the concentration of HAs. The interactive effects between copper and zinc and between lead and zinc were synergistic, while the interactive effect between copper and lead on the bioluminescence of V. fischeri was additive. The presence of HAs caused relatively high toxicity reduction in the binary mixtures of zinc and copper or zinc and lead, while the toxicity reduction in the case of the binary mixture of copper and lead was negligible.

Bioavailability and toxicity of heavy metals in the presence of natural organic matter

The effect of humic acids (HA) on the toxicity of copper, zinc and lead was investigated in this study, using the photobacterium Vibrio fischeri (Microtox test) as a test organism. The metal species and the complexation capacity of HA were predicted using model WinHumicV for speciation modeling. The toxicities of copper and lead were generally comparable, while the toxicity of zinc was lower than the ones of the other two method. The toxicity of copper decreased with the addition of HA, while the toxicity of zinc remained almost constant. The complexation of Zn with HA was low. Thus the presence of HA did not significantly influence the toxicity of Zn. For Cu and Zn, the free metal ion species showed to be basically responsible for the toxicity of these metals, while for Pb the chlorocomplexes and Pb-HA complexes contributed to the toxicity of Pb, indicating that the toxicity of heavy metals depends not only on the free metal ion species concentration but on different metal species that may be bioavailable.

Comparison of several toxicity tests applied to complex wastewaters and mussel biomarkers in receiving waters

In this study, the complex wastewaters/effluents discharged to coastal regions of Turkey and Greece were sampled, and various toxicity tests were applied. The bioassays used included the assessment of the luminescence inhibition of the bacterium Vibrio fisheri, the photosynthesis inhibition (14C uptake rate) and growth inhibition of the algal species Phaeodactylum tricornutum, and the mortality of the crustacean Artemia franciscana and rotifer Brachionus plicatilis. Additionally, "neutral red retention" and "filtration rate" sublethal biomarker techniques were performed by utilizing the mussel species Mytilus galloproviancialis, inhabiting the points of discharges in Turkey. All discharges tested were found to be acutely toxic to P. tricornutum and slightly toxic to V. fisheri, A. franciscana, and B. plicatilis. Test results showed that the 14C uptake rate toxicity test was the most sensitive one among the other bioassays. The biomarker results showed that the health status of mussels in the coastal areas decreased significantly, indicating the pollution of the receiving waters in Turkey. The conclusions drawn highlight the necessity for an intesive ecotoxicological monitoring scheme that will incorporate the most suitable bioassays and biomarkers to adequately contribute to the upgrading and maintenance of the ecological quality of the coastal waters in Greece and in Turkey.