Detection and evaluation of the fate of estrogen endocrine disrupting chemicals in wastewater treatment
Authors:   , Surujlal-Naicker Swastika 
Published: August 2021

All over the world concerns have been raised over the possible adverse effects that may occur when exposed to chemicals that have the potential to interfere and affect the endocrine system. The concern is directed at both humans and wildlife. There is still a lack of public awareness regarding Endocrine Disrupting Chemicals (EDCs) and the harmful effects on humans and wildlife. It has only been within the last decade that South Africa began the actual task for proper management and control for water and wastewater quality. There are many ways to detect these EDCs all of which are very laborious and most of the cases these EDCs are either in the pico or nano gram per litre range, too minute for many methods to detect effectively; so therefore the research project aimed to use rapid and sensitive techniques to determine the quickest means to detect the very low concentrations of theses EDCs. Two techniques were researched, i.e., Enzyme Linked immunoassays (ELISAs) and Radio-immunoassays (RIAs). The research study thus assessed the solid phase extraction (SPE) technique for total recovery of hormones; the ELISA and RIA techniques for rapid detection of natural (estrone (E1), estradiol (E2) and estriol (E3) and synthetic ethinylestradiol (EE2) by validating the precision and reproducibility . These techniques were then applied to determine hormone EDC removal first at laboratory scale investigations and then applied to full scale wastewater treatment plants (WWTP) with different configurations in order to deduce removal efficiency of each type of plant. The next phase assessed the toxicity of individual and combined estrogen standards as well as the toxicity in the WWTPs and classify and to determine if there was a correlation between hormone concentration and toxicity in final effluents. The assessment of the SPE and the immunoassay procedures (ELISA AND RIA) using standards and controls found that both these assays can be utilised to quantify hormone estrogens in wastewater. The small sample volume required reduced the labour time and application of the procedure made it cost effective and reliable techniques. The intra-assay and inter-assay validation procedures as well as the standard recoveries confirmed reproducibility and precision of the immunoassays. The % CV were <10% for both the intra-assay and inter-assay validations. The laboratory scale investigations included the operation of a modified Ludzak-Ettinger (MLE) process which enabled control and manipulation over the operational parameters in order to establish how certain parameters influenced the removal of hormone EDCs. One such parameter that was manipulated was the sludge retention time (SRT). The MLE tests showed that the SRTs definitely have an effect on the removal of hormones from the influent as well as the overall performance of sewage treatment. The 10 day SRT proved that longer SRTs will definitely aid in the removal of hormones and possibly other EDCs in raw sewage. During the 10 day SRT the influent hormone concentrations (E1: 59.11 ng/L, E2: 61.40 ng/L) were almost double than the influent hormone concentrations (E1: 26.46 ng/L, E2: 27.60 ng/L) during the 5 day SRT, which impacted on the removal efficiency. The 5 day SRT had an overall average E2 and E1 removal of 78.11% and 81.71% respectively while the 10 day SRT had average E2 and E1 removal of 91.24 % and 80.56% respectively. The 24 hour batch test provided evidence of the reversible metabolism of the E2 hormone. This was seen by the rapid decrease of E2 and the rapid increase of E1 in less than 3 hours, which proved that E2 can be metabolized in to E1. An average reduction of 94.44% of E2 was seen after 5 hours and after 10 hours was no longer detected. After 13 hours E1 could no longer be detected. This finding also provided clarity as to the lower percentage removal of E1 during the 10 day SRT of the MLE process. The Vibrio fischeri biotox method implemented was the most economic and easiest way to conduct the toxicity tests. The validation of the test used a 52.9 mg/L K2Cr2O7 standard which provided a Cr (VI) concentration of 18.7 mg/L in the final test suspension which is the theoretical effective concentration causing 50% inhibition (EC50). This specific concentration of the Cr (VI) exhibited an EC50 at 20.08 mg/L. The toxicity investigations of the individual and mixed hormone standards revealed that at the 10 ng/L concentration the individual E2 standard had the highest percentage inhibition (%INH) of 45.99% after the 30 minute contact time (T30), and when this standard was further diluted to 5 and 1 ng/L also showed higher % INH (26.04 and 23.66 %INH, respectively) than the individual EE2 standard (21.92 %INH) at 10 ng/L. . According to the toxicity classification system and after interpretation of the data, all the hormone standards were classified as Class II as they all exhibited slight acute toxicity. The 10 ng/L E2 standard had Toxicity Units (TU) of 0.8 which was close to the Class III level; however when it was in a mixture with E1 and E3, the TU was much lower (0.6 TU). The synthetic EE2 hormone also showed slight acute toxicity and had the lowest TU of 0.4. The application of the above mentioned techniques to full scale WWTPs with different configurations showed different removal efficiencies. The WWTPs ranged from the most primary consisting of just oxidation ponds to biological trickling filters, to biological nutrient removal (BNR) to conventional activated sludge (AS) plants. Removal rates ranged from 29% to 96% for E2, 0% to 89% for E1 and 0% to 100% for EE2. The overall ranking of the WWTPs from the most efficient to least efficient in terms of hormone removal were as follows: Plant E (91%) = Plant D (before UF) (91%) > Plant B (east side) (88%) > Plant B (west side) (77%) > Plant C (east side) (71%) > Plant D (after UF) (57%) > Plant A (56%) > Plant C (west side) (12%). Using the Vibrio fischeri method to evaluate the reduction of toxicity in WWTPs C, D and E proved effective. It was seen immediately after secondary biological treatment in the clarifier effluent the toxicity was reduced. Plants C, D and E had reduced the toxicities by 100, 80 and 97 % immediately after secondary biological treatment, while after the addition of the Chlorine disinfectant in the final stage of treatment the toxicity increased having %INH of 99.9, 15.7 and 99.9 respectively. In conclusion the SPE can be used as an extraction procedure for hormones in wastewater and the immunoassays can be used as rapid techniques for quantification of hormone EDCs in wastewater. The ELISA technique proved to be the slightly superior to the RIA in terms of facilities required. The laboratory scale procedures proved that some hormones can be oxidised to other hormones and therefore longer sludge retention times may be required to improve the removal. The study of the different WWTPs configuration showed that plant configuration and operational parameters impact the removal of hormone EDCs. The composition of the influent received by the plant also has an effect on the removal, i.e., whether it’s industrial, domestic or a mixture of both. Results concluded that plants which have either mixing and/or aeration with activated sludge and longer SRTs of more than 10 days have a higher rate of hormone removal than those plants with shorter SRTs and that the activated sludge processes were capable of reducing the toxicity of the influent. Overall results indicated that hormone EDCs are indeed being discharged with the effluents from WWTPs in South Africa. However whether the concentrations left in the final effluents will still have an adverse effect on the aquatic life is a question that still remains unanswered. The aquatic ecosystems are inevitably being polluted with these EDCs and their breakdown products.