Developmental toxicity of p,p′‐dichlorodiphenyltrichloroethane, 2,4,6‐trinitrotoluene, their metabolites, and benzo[a]pyrene in Xenopus laevis embryos

Abstract

Since 1995, high incidences of deformed frogs have been documented in Kitakyushu, Japan. In this area, relatively high concentrations of DDT, trinitrotoluene (TNT), their metabolites (p,p'-dichlorodiphenyldichloroethylene [DDE], p,p'-dichlorodiphenyldichloroethane [DDD], 2-amino-4,6-dinitrotoluene [2ADNT], and 4-amino-2,6-dinitrotoluene [4ADNT]), and benzo[a]pyrene [BaP]) have been identified from field samples. I used a standardized assay with Xenopus laevis embryos (frog embryo teratogenesis assay--Xenopus, FETAX) to examine the developmental toxicity of these compounds. Both DDE and BaP were considered nearly nontoxic in embryonic development because they induced low (< 10%) mortality and malformation incidence even at the highest concentrations tested (DDE, 393 microM; BaP, 13.2 microM). The DDD (96-h median lethal concentration [LC50] = 44.1 microM, 96-h median effective concentration [EC50] for malformation = 14.9 microM) was more lethal and teratogenic than its parent compound, DDT (96-h LC50 = 101 microM, 96-h EC50 = 41.5 microM). Predominant symptoms observed were axial malformations (DDT and DDD) and irregular gut coiling (DDT). However, DDT and DDD should not act as major lethal or teratogenic toxicants in the aquatic environment within a short-term exposure via water because their 96-h LC50 and 96-h EC50 values were extremely high, considering their low solubility in water. The TNT (96-h LC50 = 16.7 microM) was more lethal than 2ADNT (96-h LC50 = 166 microM) or 4ADNT (96-h LC50 = 115 microM). Although 4ADNT (96-h EC50 = 85.8 microM) induced various tadpole malformations, it was a weak teratogen compared with TNT (96-h EC50 = 9.78 microM) and 2ADNT (96-h EC50 = 16.9 microM). The most typical malformations observed were axial malformations, eye abnormalities (TNT), edema, and irregular gut coiling (2ADNT and 4ADNT). The 96-h LC50 and 96-h EC50 values of TNT, 2ADNT, and 4ADNT were lower than their saturated concentrations in water. Therefore, these nitroaromatic compounds may show lethal or teratogenic effects on aquatic animals if their habitats are severely contaminated with TNT.

Review and synthesis of evidence regarding environmental risks posed by munitions constituents (MC) in aquatic systems

“…Sublethal effects on malformation were observed at much lower concentrations, with EC50 values of 2.2, 3.3, and 16.9 mg/L for TNT, 2-A-2,4-DNT, and 4-A-2,6-DNT, respectively (Saka 2004). Growth was also affected at sublethal concentrations of those MC.…”

“…For tadpoles of the African clawed frog (Xenopus laevis), the 4-day LC50 value for TNT (3.8 mg/L) was substantially lower than that for 2-A-2,4-DNT (32.7 mg/L) or 4-A-2,6-DNT (22.7 mg/L) (Saka 2004) (Figure 66). Sublethal effects on malformation were observed at much lower concentrations, with EC50 values of 2.2, 3.3, and 16.9 mg/L for TNT, 2-A-2,4-DNT, and 4-A-2,6-DNT, respectively (Saka 2004).…”

Bioconcentration and metabolism of pesticides and industrial chemicals in the frog

“…56) Very similar profiles in uptake and depuration resulted in almost the same BCF values for three organochlorines. Since DDE was nearly non-toxic in the embryonic development of X. Laevis but DDD was more lethal and teratogenic than DDT, 57) the bioconcentration profiles of these metabolites should be examined similarly to DDT from a toxicological viewpoint by considering the developmental stage of the frog. The toxicological concern about an environmentally more persistent metabolite was reported for fipronil.…”

Summary Review of the Aquatic Toxicology of Munitions Constituents

“…Several studies reported the toxicity of MC to a variety of freshwater fish, including fathead minnows, channel catfish, and zebrafish (reviewed in Talmage et al 1999 andNipper et al 2009; see also Mukhi et al 2005;Mukhi and Patino 2008;Gust et al 2011), as well as to frog larvae (Saka et al 2004;Paden et al 2011). In contrast, adverse biological effects of MC were reported for only two marine fish species (Nipper et al 2001;Lotufo et al 2010a,b,c).…”