Luminous degradation and foliage retention of dyes FD&C Blue no. 1 and FD&C yellow no. 5 used as spray tracers

摘要

Three trials were carried out at Núcleo de Pesquisas Avançadas em Matologia (NUPAM), FCA/UNESP – Campus de Botucatu, SP, Brazil, to evaluate the stability of dyes FD&C Blue no. 1 and FD&C Yellow no. 5 when exposed to different periods of solar light and Eichhornia crassipes leaf contact. Solutions at 0,3125, 0,625, 1,25, 2,5, 5, 10 and 20 ppm of both dyes were prepared and conditioned into Quartz tubes hermetically closed and submitted to several solar light and darkness periods, as follows 0; 0,5; 1; 2; 4; 6 and 10 hours. Samples of 10 mL were collected from the tubes after the end of each period and left to posterior analysis. The second trial treatments were designed as a factorial 2x7: 2 light conditions (sunlight or darkness) and 7 exposure timings (0; 0,5; 1; 2; 4; 6 and 10 hours), with six replications. Eight drops of 5 µL of FD&C Blue no. 1 and FD&C Yellow no. 5 solutions at 4,000 ppm were placed on glass Petri dishes, using a micropipette. Petri dishes were washed with 50 mL of distilled water immediately after each exposure period ending to extract the dyes deposited on it. The same treatments were used in the third trial, with four replications. However, the coloring solutions were dropped on Eichhornia crassipes foliar surfaces. The same dye extraction procedures were also used after each exposure period ending. The final solutions obtained from the three trials were submitted to absorbance optical analysis at spectrophotometer UV-Visible on wave length of 630 and 427 nm for FD&C Blue no. 1 and FD&C Yellow no. 5 dyes, respectively. Both coloring solutions at different concentrations were not degraded by solar light after being submitted to each exposure period of sunlight incidence into the Quartz tubes (closed situation), since recovering curves showed practically the same equations when compared to the dye solutions kept under darkness conditions. The same stability was observed when the dye solutions were submitted to sun light incidence in open ambient, i.e., on Petri dishes. FD&C Yellow no. 5 showed high stability when dropped over E. crassipes leaves, regardless of the light condition. However, statistical losses of 7.8% and 16.8% were observed when FD&C Blue no. 1 was dropped over the surface of water hyacinth leaves during 10 h under darkness and sunlight incidence conditions, respectively.