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In accordance with the proposed structures of OXC and its degradation by-products, their eco-toxicities were preliminarily estimated with the US-EPA TEST. TEST can predict eco-toxicity by relating the biological activity of chemicals to theoretically calculated or experimental descriptors of their chemical structure, according to the global QSAR models (Rodríguez-Álvarez et al. 2013). Table 2 presents those estimated values for fathead minnow LC50 (96 h), Daphnia magna LC50 (48 h) and oral rat LD50 of OXC as well as its degradation by-products. The predicted toxicity values of −log(LC50) or −log(LD50) according to the QSAR models, displayed as −log(mol L−1) or −log(mol kg−1), as well as their calculated LC50 or LD50 values (mg L−1 or mg kg−1) were obtained. Results indicated that most OXC degradation by-products showed higher toxicity than OXC for at least one test. For OXC chlorination, CL-1, CL-2, CL-6, CL-7, CL-9 and CL-10 were more toxic than OXC for two tests. CL-5 and CL-8 were predicted more toxic than OXC for all the tests. This may be particularly relevant for CL-5, CL-6, CL-7, CL-8 and CL-10, as being the most accumulated by-products during chlorination, would pose a potential risk to drinking water quality. For OXC ClO2 oxidation, CD-1, CD-2 and CD-5 showed higher toxicity than OXC for more than two tests, in which only CD-2 and CD-5 showed accumulative tendency during ClO2 oxidation. Hence, ClO2 oxidation was predicted to have less toxic by-products than chlorination. For OXC ozonation, O-1, O-7, O-8, O-9 and O-10 were predicted more toxic than OXC for more than two tests, especially O-9 and O-10, being the most accumulated by-products during ozonation, showing 3.05 times more toxicity than OXC for Daphnia magna LC50 (O-9) and 4.32 times more toxicity than OXC for fathead minnow LC50 (O-10), respectively.

Table 2

US-EPA TEST of predicted toxicological LC50 and LD50 values of OXC and its degradation by-products

 Fathead minnow LC50 (96 h)
Daphnia magna LC50 (48 h)
Oral rat LD50
Compounds− log (mol L−1)mg L−1−log (mol L−1)mg L−1−log (mol kg−1)mg kg−1
OXC 4.42 9.53 5.23 1.50 2.10 2,000.03 
CL-1 (CD-1) 4.62 6.39 5.41 1.04 2.10 2,124.94 
CL-2 4.49 8.63 5.22 1.60 2.30 1,350.79 
CL-3 (CD-3, O-2) 4.76 4.60 5.18 1.77 2.03 2,494.82 
CL-4 (CD-4, O-3) 4.27 15.01 5.66 0.62 2.10 2,244.96 
CL-5 (CD-5) 4.89 2.89 5.26 1.24 2.63 522.87 
CL-6 5.40 0.77 5.09 1.60 2.52 590.69 
CL-7 5.10 1.81 NAa NA 2.33 1,064.61 
CL-8 5.66 0.50 5.73 0.43 2.53 670.59 
CL-9 5.15 2.02 6.33 0.13 1.97 3,044.25 
CL-10 5.42 1.23 5.55 0.91 1.78 5,283.93 
CL-11 5.01 2.82 NA NA NA NA 
CD-2 (O-1) 5.02 2.55 4.44 9.63 2.66 585.78 
CD-6 5.36 1.31 NA NA NA NA 
O-4 NA NA 5.15 2.13 1.74 5,449.15 
O-5 4.32 14.47 4.98 3.18 1.68 6,312.40 
O-6 4.92 3.82 5.19 2.05 1.79 5,124.54 
O-7 5.01 2.74 5.57 0.77 2.49 911.60 
O-8 5.07 2.54 5.16 2.05 2.52 901.23 
O-9 3.98 26.73 5.84 0.37 2.12 1,933.45 
O-10 5.00 1.79 4.35 8.10 2.05 1,611.18 
 Fathead minnow LC50 (96 h)
Daphnia magna LC50 (48 h)
Oral rat LD50
Compounds− log (mol L−1)mg L−1−log (mol L−1)mg L−1−log (mol kg−1)mg kg−1
OXC 4.42 9.53 5.23 1.50 2.10 2,000.03 
CL-1 (CD-1) 4.62 6.39 5.41 1.04 2.10 2,124.94 
CL-2 4.49 8.63 5.22 1.60 2.30 1,350.79 
CL-3 (CD-3, O-2) 4.76 4.60 5.18 1.77 2.03 2,494.82 
CL-4 (CD-4, O-3) 4.27 15.01 5.66 0.62 2.10 2,244.96 
CL-5 (CD-5) 4.89 2.89 5.26 1.24 2.63 522.87 
CL-6 5.40 0.77 5.09 1.60 2.52 590.69 
CL-7 5.10 1.81 NAa NA 2.33 1,064.61 
CL-8 5.66 0.50 5.73 0.43 2.53 670.59 
CL-9 5.15 2.02 6.33 0.13 1.97 3,044.25 
CL-10 5.42 1.23 5.55 0.91 1.78 5,283.93 
CL-11 5.01 2.82 NA NA NA NA 
CD-2 (O-1) 5.02 2.55 4.44 9.63 2.66 585.78 
CD-6 5.36 1.31 NA NA NA NA 
O-4 NA NA 5.15 2.13 1.74 5,449.15 
O-5 4.32 14.47 4.98 3.18 1.68 6,312.40 
O-6 4.92 3.82 5.19 2.05 1.79 5,124.54 
O-7 5.01 2.74 5.57 0.77 2.49 911.60 
O-8 5.07 2.54 5.16 2.05 2.52 901.23 
O-9 3.98 26.73 5.84 0.37 2.12 1,933.45 
O-10 5.00 1.79 4.35 8.10 2.05 1,611.18 

aNA: No reliable prediction was obtained.

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