Comparative study of plant growth hormone (herbicide) toxicity in various biological subjects

Abstract

Due to their widespread distribution and toxic nature, herbicides may have a serious impact on the environment and exert adverse effects on associated organisms. The present study was conducted to determine the acute toxicological effects of some plant growth hormones used as herbicides on four biological subjects and compare the subjects' sensitivity to individual testing substances. The herbicides 4-(indol-3-yl)acetic acid C 10H 9O 2N (IAA), N 6-( β 2-isopentenyl)adenosine (π-indolylpropionic acid) C 11H 11O 2N (IPA), 2,4-dichlorophenoxyacetic acid C 8H 6O 3Cl 2 (2,4-D), 4-chloro-2-methylphenoxyacetic acid C 9H 9O 3Cl (MCPA), and 1,napthylacetic acid C 12H 10O 2 (NAA) were tested and the following biological subjects were used: Daphnia magna, Tubifex tubifex, Scenedesmus quadricauda, and seeds of Sinapis alba. For S. alba, the influence of herbicides on seed germination (G) and root growth inhibition (I) was observed. For T. tubifex, the tests lasted 96 hr, for D. magna 48 hr, for S. quadricauda 20 days, and for S. alba 72 hr. The rank order of toxicity of herbicides used for T. tubifex was NAA > IAA > IPA > 2,4-D > MCPA; for D. magna. NAA > IAA > IPA > MCPA > 2,4-D; for S. quadricauda, IAA > IPA > NAA > MCPA > 2,4-D; for S. alba seed germination, NAA > IPA > 2,4-D > MCPA > IAA; and for root growth inhibition. NAA > 2,4-D > MCPA > IAA > IPA. When the sensitivity of tested organisms to individual herbicides was studied from LC 50 and EC 50 values, the following rank orders of sensitivity were obtained: for IAA, it was S. alba (I) > S. quadricauda > T. tubifex > D. magna > S. alba (G); for 2,4-D, it was S. alba (I) > S. quadricauda > T. tubifex = S. alba (G) > D. magna; for MCPA, it was S. alba (I) > S. quadricauda > T. tubifex = D. magna = S. alba (G); for IPA, it was S. alba (I) > T. tubifex > S. quadricauda > D. magna = S. alba (G); and for NAA, it was S. alba (I) > S. quadricauda > T. tubifex > S. alba (G) > D. magna.