## 3 Results and Discussion
### Toxicity Analysis  
Diclofenac is classified by the EU Directive 93/67/EEC as \"harmful to aquatic organisms\" [54; 55] and due to its low log K\({}_{\text{ow}}\) of 4.51 as toxic [56]. The EC\({}_{50}\) toxicity towards _Vibrio fischeri_ was determined to be 19.7 mg L\({}^{-1}\) (with a confidence interval of 17.9 to 22.2) which is comparable to literature value (15.78 mg L\({}^{-1}\)[56]). As it can be seen in Figure 8, the toxicity towards _Vibrio fischeri_ increases with ongoing phototransformation until 90 min of irradiation. Diclofenac completely transforms within the first 90 min of UVA irradiation. The phototransformation products are more toxic towards _Vibrio fischeri_ than diclofenac itself. The toxicity unit (TU = 100/EC\({}_{50\%}\), EC\({}_{50\%}\) is the effect concentration at which 50% of effect occurs; the higher the TU, the higher the toxicity) and G\({}_{\text{L}}\) level (dilution level at which the inhibition is below 20% for the first time; the higher the G\({}_{\text{L}}\) level, the higher the toxicity) at 90 min of UVA irradiation doubles compared to an untreated diclofenac solution. The evaluation of the toxicity of diclofenac treated with UVA light is controversial discussed [52; 56; 57; 58]. But the conditions (concentration of diclofenac, UVA light wavelength, UVA light intensities, additives in water, tested biological organism) do differ and lead to different transformation products and concentrations of these products. [PERSON] et al. [57] and [PERSON] et al. [52] identify a decrease of toxicity towards _Vibrio fischeri_ after sunlight and UVA (365 nm) light treatment, respectively. Contrary, [PERSON] [58] studies showed an increase of toxicity towards the algal _S. vacuolatus_ after day light treatment. A carbazole-type compound and diphenylamine derivates, which are generated during phototransformation of diclofenac, were identified to be the toxic transformation products. The toxicity increases regarding TU (50% effect) for the phototransformation during the first 90 min with and without PVDF is similar. The toxicity shift regarding G\({}_{\text{L}}\) levels (20% inhibition) is slightly different analyzing diclofenac irradiation with and without PVDF. After 30 min of UVA irradiation with PVDF the G\({}_{\text{L}}\) is two levels higher, thus more toxic and only 16.66% of volume fraction is needed to gain a 20% inhibition compared to 25% of volume fraction without PVDF. After 90 min of photoreaction the G\({}_{\text{L}}\) level is lower for the solution with PVDF compared to without PVDF (G\({}_{\text{L}}\) level 8 to 6, respectively), thus the toxicity is reduced with PVDF. After 18 h of photoreaction with  
Figure 8: (a) Change of toxicity to _Vibrio fischeri_ after irradiation of diclofenac with UVA light with and without PVDF (left axis) expressed in toxicity units (TU = 100/EC\({}_{50\%}\), EC\({}_{50\%}\) is the effect concentration at which 50% of effect occurs; the higher the TU, the higher the toxicity). The concentration decrease of diclofenac after irradiation was analyzed via HPLC (right axis). In (b) is the toxicity towards _Vibrio fischeri_ after irradiation of diclofenac with UVA light expressed in G\({}_{\text{L}}\) levels. The G\({}_{\text{L}}\) value is the dilution level at which the inhibition is below 20% for the first time (the higher the G\({}_{\text{L}}\) level, the higher the toxicity). All values below 20% inhibition are normal test fluctuations. Level 1 (80% volume fraction), level 4 (25% volume fraction), level 6 (16.66% volume fraction), level 8 (12.5% volume fraction). PVDF the toxicity declines. An EC\({}_{50\%}\) value could not be evaluated, and the G\({}_{\mathrm{L}}\) level is 1. The 18 h UVA light treated diclofenac solution without PVDF shows towards _Vibrio fischeri_ a higher toxicity (regarding TU and G\({}_{\mathrm{L}}\)) than the untreated diclofenac solution. Phototransformation product X (see Figure 2 in Section 3.1. for the structural formula), which is a diphenylamine derivative [58], might be one of the toxic products.