Objective This research aims to investigate the effects of chronic exposure of lettuce (Lactuca sativa) to environmentally relevant concentrations of dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) on its photosynthetic characteristics and consumption safety,to provide a theoretical basis for evaluating the potential risks of chloroacetic acid-based disinfection byproducts (DBPs) in irrigated agriculture. Method Using loose-leaf lettuce as the test materials,a soil culture experiment was conducted.Irrigation was performed for 35 days with aqueous solutions of DCAA and TCAA at different mass concentrations (10,40,70 and 100 μg/L).The growth characteristics and photosynthetic physiological properties of lettuce were determined under different treatments,and the bioconcentration factor (BCF),transport factors (TF),and health risks of consuming lettuce of DCAA and TCAA in lettuce were also analyzed. Result Compared with the control group,in both the DCAA and TCAA (10,40,70 and 100 μg/L) groups,the fresh mass of lettuce leaves decreased significantly by 23.13%-41.46% and 10.00%-28.00%,respectively,but there was no significant difference in the height and leaf area of the plant.In DCAA (70 and 100 μg/L) groups,the fresh root mass,the total surface area of the roots,average root diameter and total root volume were significantly decreased by 70.66%-73.88%,46.52%-69.70%,24.14%-26.37% and 67.79%-78.85%,respectively,which were generally higher than those in the TCAA treatment group(66.38%-66.81%,54.75%-55.78%,13.36%-16.44%,and 64.42%-64.90%).Under 10 μg/L DCAA treatment,the root fresh mass of lettuce was significantly decreased by 28.69%.Under 10 μg/L TCAA treatment,no significant difference was observed in the root fresh mass.In contrast,the net photosynthetic rate (Pn) and intercellular CO2 concentration (Ci) of lettuce were significantly reduced by 45.08%-63.19% and 13.00%-27.68% in the TCAA (40,70,and 100 μg/L) group,which were higher than those in the DCAA treatment group(30.10%-39.09% and 11.49%-18.52%).The enrichment and transfer characteristics of the pollutants showed that the accumulation of DCAA and TCAA in lettuce had a threshold effect,and the peak values of BCF and TF were observed in the 70 μg/L irrigation group.The risk index (RI) of lettuce consumption increased with the increase of DCAA and TCAA irrigation concentration,but remained lower than 1 in both cases. Conclusion The damage to lettuce root morphology by chronic exposure to environmentally relevant concentration of DCAA was prominent,whereas TCAA showed stronger photosynthesis toxicity.Although the risk index for DCAA and TCAA did not exceed the threshold,the reduced photosynthetic capacity and root structure damage in lettuce indicate that chronic exposure (≥40 μg/L) will significantly impair the plant’s physiological functions and yield.
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