What threshold of urinary cadmium (Cd-U) is currently considered indicative of early renal tubular dysfunction in exposed adult populations?

 I am conducting a study on chronic environmental cadmium exposure and its nephrotoxic effects, particularly focusing on early biomarkers of renal tubular damage. Several sources suggest 2 µg/g creatinine as a reference point, but variability exists depending on population, sex, and co-exposure.
 Could experts clarify which threshold (e.g. 1 µg/g, 2 µg/g, or 5 µg/g creatinine) is most reliable or currently used in risk assessments and clinical practice?