Kaolin

As in previous studies (Ishikawa et al., 2019 (link); Nakabayashi et al., 2016 (link); Sasaki et al., 2021 (link)), rats in the arthritis, diclofenac, LIPUS, and phonophoresis groups were injected with 300 μl of a mixture of 3 % kaolin (Wako Pure Chemical Industries, Ltd. Osaka, Japan) and 3 % carrageenan (Sigma Chemical Co., St. Louis, MO, USA) into the right knee joint anteriorly under anesthesia. In this arthritis model, the erythrocyte sedimentation rate significantly increased 1 day after injection and returned to baseline 7 days after injection (Sasaki et al., 2021 (link)). Therefore, we defined 7 days post-injection as the acute phase of this model. In the control group, 300 μl of saline was injected as a sham treatment.

Benzo[a]pyrene (>97.0% purity, Chemical Abstracts Service [CAS] no. 50‐32‐8), CPS (>99.0% purity, CAS no. 2921‐88‐2), Phe (>99.0% purity, CAS no. 85‐01‐8), Pyr (>98.0% purity, CAS no. 129‐00‐0), acetone (>99.5% purity), acetonitrile (>99.8% purity), and kaolin (practical grade) were purchased from FujiFilm Wako Pure Chemicals. Chlorpyrifos‐d₁₀ was purchased from Kanto Chemical. Quartz sand (0.2–0.8 mm particle ≥40%, loss on ignition at 900 °C ≤0.05%) was purchased from Merck. Peat was purchased form Midori, which was collected from Hokkaido, Japan. The elemental composition of the peat as determined by an elemental analyzer (Flash EA1112; Thermo Fisher Scientific) was as follows: N 1.5% w/w, C 37.6% w/w, H 4.4% w/w.