GB/T 45238-2025 in English

In-depth interpretation of GB/T 45238-2025 standard

1. Background and significance of standard formulation

In order to improve the predictive ability of the bioaccumulation of chemicals in fish, this standard establishes an in vitro intrinsic clearance determination method based on the S9 subcellular fraction (RT-S9) of rainbow trout liver. This method combines the OECD test guidelines and determines the clearance rate constant of the test substance by the substrate clearance method, providing key data for the computer toxicokinetic model.

2. Comparative analysis of standard frameworks

3. Recommendations for standard implementation

4. Technical points in the standard

Explanation of key terms:

• Intrinsic clearance (C_{LINVITRO, INT}):The rate at which a unit enzyme or cell metabolizes a test substance per unit time under in vitro conditions.
• First-order clearance kinetics:A chemical reaction characteristic in which the rate of substrate molecule clearance is proportional to its concentration.
• S9 subcellular fraction:A cell-free system derived from liver tissue containing cytoplasmic and microsomal enzymes, mainly including CYP, GST and other metabolic-related enzymes.

Actual application case:

A laboratory used this standard to test a new pesticide and determined its intrinsic clearance by RT-S9. The experimental results showed that the clearance rate of the pesticide under in vitro conditions was 0.08 h⁻¹, which met the linear range required by the standard (R²≥0.85). Combined with the PBTK model prediction, it provides key data for evaluating its bioaccumulation potential.

5. Key points of chart description