Typical time courses for BPA and BPF degradation measured using the TOC and SDA methods in January and October are shown in . Faster degradation followed shorter lag periods, as measured using the SDA method. The lag periods for all experiments degrading BPA using the SDA method were between 0–15 days and the microcosms exhibited degradation within 3–12 days. 6–12 days were needed for degradation following a lag period of 3–21 days for all experiments degrading BPF using the SDA method.
Typical time courses for bisphenol A and F (BPs) biodegradation in January (A) and in October (B) for South port samples. Top: Sea die-away method (SDA). Bottom: TOC Handai method (TOC).
The lag periods for the 2 samples degrading BPA using the TOC method were between 6 and 12 days, and the degradation times between 12 and 21 days, whereas microcosms exhibited long lag periods (12–45 days) as well as long degradation times (9–39 and more days) for BPF degradation. The BPs’ concentrations in the control samples of both methods did not change noticeably. Furthermore, the BPS concentration remained unchanged over the test period of 60 days in the TOC and SDA samples. BPA was hardly degraded using the TOC method. No test (out of six) showed BPA degradation in the North port samples while two out of six of the South port samples (33% degradation efficiency) could degrade BPA using the TOC method. and represent degradation efficiencies of BPA, BPF and metabolites. Degradation tests for the North port samples showed no BPF reduction (four samples) in December and October experiments and partial and complete degradation for the two samples in the January experiments, representing 17% BPF degradation efficiency in the North port tests as measured by the TOC method. BPF showed 83% degradation efficiency and was degraded in five out of six TOC samples, out of which two showed BPF depletion within 30 days in the South port tests. In general BPF could be degraded in all but one sample in the South port experiments and according to both methods within 48 days. All the SDA samples degraded BPA (six samples) and BPF (seven samples) within 30 days in the South port tests. Degradation efficiencies were similar for BPA and BPF and both sampling points as measured by the SDA method, except for the January experiments in which no depletion of BPA (two samples) could be detected in the North port tests.
Degradation of bisphenol A (BD) and its metabolites (MD) as measured by the TOC Handai (TOC) and the Sea die-away (SDA) methods and monitored by HPLC.
Degradation of bisphenol F (BD) and its metabolites (MD) as measured by the TOC Handai (TOC) and the Sea die-away (SDA) methods and monitored by HPLC.
Thus four tests out of six depleted BPA (67% degradation efficiency) in the North port sampled water using the SDA method. The North port samples exhibited better BPF degradation using the SDA method than using the TOC method and 83% BPF degradation efficiency were measured by the SDA method. According to the SDA method four samples (out of six) degraded BPF completely in the North port microcosms during a 30-days-period. One of two samples that showed little and partial degradation was degraded on day 42, but for the other sample further data is missing because monitoring was stopped on day 30. Summarizing the results for BPA and BPF for both sampling sites and using both methods we find an overall biodegradation efficiency of 8% in the North port and 58% in the South port tests as measured by the TOC method and 75% in the North port and 100% in the South port tests as measured by the SDA method.
Because of the difference in water temperatures () experiments can be split into two experimental seasons for the data interpretation in this study: ‘Winter’ for January and December and ‘Summer’ with high water temperatures for October. Comparison of summer and winter experimental data shows that BPF was degraded in approximately half of the microcosms according to the TOC method (four completely plus one incompletely degraded sample out of eight in winter compared with two completely degraded samples out of four in summer) during both seasons. Thus degradation efficiencies were 50% in winter as well as in summer for BPF as measured by the TOC method. However, little degradation of BPA was observed in winter (13% efficiency) as well as in summer (25% efficiency) tests using the TOC method. Using the SDA method hardly any seasonal degradation differences of BPF were measured and its overall biodegradation efficiency was 92% due to one sample that was withdrawn on day 30. Data showed that the sample was likely to have degraded in less than one more week, so biodegradation efficiencies for BPF should be 100% for summer as well as for winter. BPA degradation in winter (75% efficiency) was less efficient than in summer with 100% degradation efficiency: two of the winter microcosms (four) did not degrade the compound according to the SDA method.
Metabolites were detected during BPA degradation and the TOC samples had more metabolites than the SDA samples in December and October (). Winter experiments had a peak at 2.4 min in common and a peak at 2.6 min was detected for the TOC experiments in December as well as for the SDA experiments in January. The tR differed between summer and winter experiments. However, all the SDA samples’ metabolites had the same tR as the TOC samples’ metabolites in October, excluding the latest at 3.6 min (TOC) and 4.6 min (SDA) and adding two for the TOC method.
BPA metabolite list for a 60 days test period.
The metabolites with tR between 2.2–2.7 min in the TOC December experiments were not degraded within 60 days, whereas the metabolites with tR of 2.0, 2.5, 3.4 and 4.6 min were found to be persistent in the October experiments according to the SDA method.
Generally, October experiments showed more metabolite peaks than all other experiments for BPA as well as for BPF (). According to the SDA method more metabolite peaks occurred during BPF degradation than the TOC method in October. The TOC and the SDA results showed metabolite peaks in common at 2.0 and 2.2 min in October. Ultimately, the only metabolite that persisted had a tR of 2.3 min in the TOC experiment in January. The sample showed poor BPF degradation as well.
BPF metabolite list for a 60 days test period.
Metabolite peaks occurring during BPA and BPF degradation overlapped with the peaks of benzoquinone, hydroquinone or hydroxybenzoic acid but could not be clearly identified as such through chromatogram comparison or spiking. The metabolite peak detected at tR = 2.6 min occurring during BPF degradation could be identified as dihydroxybenzophenone through chromatogram comparison and spiking of the sample with dihydroxybenzophenone.
Analytical results for partial and complete degradation of the BPs are compared in and . The time-frame of occurring metabolites is depicted. In samples with complete degradation of BPs as well as metabolites, no corresponding peaks were ultimately detected.
HPLC chromatogram showing BPA degradation and metabolites in seawater with partial degradation (A) and complete degradation (B). Day (d) of sampling is given.
HPLC chromatogram showing BPF degradation with metabolites in seawater with partial degradation (A) and complete degradation (B). Day (d) of sampling is given.
Results in other experiments revealed BPA and BPF metabolite peaks occurring at tR later than the HPLC-program run times of 6.0 (BPA) and 4.5 (BPF) min. The run times were extended in the October experiments and peaks at tR = 10.0 (BPA experiments) and tR = 4.6 min (BPF experiments) were recorded regularly. These peaks were depleted at the same time or before the parent compounds. The observed peaks remained unchanged in samples showing no degradation, including the control samples. In one TOC and two SDA samples metabolites with tR of 4.6, 5.6 and 5.9 min were detected that depleted within 30 days.
Summarizing the results in , we see that BPA and BPF were degraded more easily using the SDA method. All samples degraded the compound added in the SDA experiments except for the winter samples, in which half of the BPA tested microcosms did not exhibit any degradation, and except for the BPF sample for which the experiment was terminated on day 30. Biodegradation efficiencies were more than 92% for BPF and 83% for BPA in the SDA experiments. Using the TOC method a difference in BPA and BPF degradation ability of the microcosms is apparent. BPA degradation occurred in two out of 12 samples (17% degradation efficiency) whereas BPF degradation occurred in six out of 12 samples (50% efficiency).
Summary of results for a 60 day monitoring period.