Permissible but not protective: 11-year cohort evidence linking respirable rubberwood dust exposure to lung function decline in Thai workers

• First 11-year cohort linking rubberwood dust exposure to lung function decline in tropical workers. • Each 1 mg·year/m³ CE increase reduced FEV₁ by –4.90 ± 0.79 mL/year ( p < 0.001). • Age >35 lost an additional –10.10 mL/year ( p < 0.001); light smokers lost –5.44 mL/year ( p = 0.03). • Declining occurred below Thailand’s 5 mg/m³ limit, revealing regulatory insufficiency. • Supporting revising exposure limits and strengthening respiratory protection in LMICs. Respirable wood dust is a known occupational hazard, yet longitudinal evidence from tropical hardwoods, particularly rubberwood, a major Southeast Asian export, remains scarce. Most existing data are cross-sectional or based on temperate wood species, limiting relevance to local policy. To quantify the long-term impact of cumulative exposure (CE) to respirable rubberwood dust on lung function decline and identify high-risk subgroups among Thai furniture workers. An 11-year retrospective cohort (2012–2023) of 235 exposed and 137 reference workers was analyzed. CE was calculated as time-weighted average dust concentration × employment years. Annual changes in FEV₁ and FVC were estimated using multivariable linear regression, adjusting for age, sex, BMI, smoking, and asthma. Mean respirable dust exposure was 0.40±0.20 mg/m³ in exposed workers vs. 0.07 ± 0.02 mg/m³ in references ( p < 0.001), both below Thailand’s permissible exposure limit (5 mg/m³). Workers with CE >4.44 mg·year/m³ showed significantly greater FEV₁ decline: -11.40±4.04 mL/year in nonsmokers ( p = 0.005) and -17.40±4.94 mL/year in smokers ( p < 0.001). Each 1 mg·year/m³ CE increase was linked to a -4.90±0.79 mL/year FEV₁ reduction ( p < 0.001), robust in sensitivity modeling (β= -4.29±0.82; p < 0.001). Age >35 lost an additional -10.10 mL/year ( p < 0.001), and even light-smoking (<7 pack-years) had a greater decline (-5.44 mL/year; p = 0.03), highlighting increased vulnerability with age and smoking. FVC trends were inconsistent. Although within the permissible limit, respirable rubberwood dust exposure causes measurable lung function loss. The current threshold is clearly not protective. A revised, wood-specific standard is urgently needed to prevent irreversible respiratory harm in tropical settings.