Biochemical Effects of Chlorpyrifos on Two Developmental Stages of Xenopus Laevis

Abstract

Abstract-The effects of a 96-h static exposure to chlorpyrifos were examined in two developmental stages of larval Xenopus laevis (premetamorph and metamorph). Measures of effect included mortality, deformity, cholinesterase (ChE) activity, and DNA and protein concentration. All parameters indicated that metamorphs were more sensitive than were premetamorphs. For larvae exposed as premetamorphs, the median lethal concentration and median effective concentration were 14.6 mg/L and 1.71 mg/L; for those exposed as metamorphs, values were 0.56 mg/L and 0.24 mg/L, respectively. Cholinesterase activity was the most sensitive biochemical parameter. Exposure to chlorpyrifos at 0.01 mg/L caused significant decreases in the ChE activity of metamorphs; 0.1 mg/L significantly decreased premetamorph ChE activity. Metamorph DNA was significantly decreased at 0.1 mg/L; premetamorph DNA was not reduced until exposure to 1.0 mg/L. Whole-body protein was the least sensitive biochemical measure of effect. Premetamorphs did not experience a reduction in protein concentrations. Metamorph protein concentration was significantly decreased at 1.0 mg/L. Based on current surface water data, the most sensitive effect would not have a high probability (< or = 4.2%) of occurring in the environment.

Cholinesterase activity and behavior in chlorpyrifos‐exposed Rana sphenocephala tadpoles

“…Chlorpyrifos toxicity is not only species‐specific in amphibians but there is also an indication that larval development stage has a considerable influence on toxicity. Specifically, Richards and Kendall [15] determined the 96‐h LC50 for two developmental stages of X. laevis tadpoles and found early stage larvae (Nieuw‐koop and Faber [N/F] stage 14 [27]) to have a value of 14,600 μg/L, whereas older larvae (N/F stage 46) had a value of 560 μg/L.…”

Risks to Aquatic Organisms from Use of Chlorpyrifos in the United States

“…Where several stages of the same species were tested, the more sensitive stage (based on the EC or LC value) was used. For example, data from larval amphibians were selected over embryos, which are generally less sensitive (Richards and Kendall 2002 ). The details of toxicity data included and excluded from SSDs are indicated in SI Table 1.…”

Survival, development, and gonadal differentiation in Rana dalmatina chronically exposed to chlorpyrifos

“…From literature, it is known that chlorpyrifos can be highly toxic to aquatic invertebrates and fish, acute risks for amphibian tadpoles were also of concern based on peak estimated environmental concentrations (Giesy et al, '99; EPA, 2000; Carriger and Rand, 2008). Furthermore, an apparent connection between the presence of chlorpyrifos residues and reductions in amphibian populations has been reported at both local (Fellers et al, 2004) and landscape scales (Davidson et al, 2001; Sparling et al, 2001); nevertheless, there is a lack of knowledge regarding the effects of chlorpyrifos on amphibians (Giesy et al, '99; Richards and Kendall, 2002, 2003). …”