Do environmental regulation policies induce boundary effects: evidence from hog production in the Yangtze River Basin, China

Although environmental regulations are intended to improve ecological conditions, their implementation may also be accompanied by a relative concentration of polluting activities in boundary areas, thereby increasing pollution pressure in these locations. Hog production has long been a major contributor to water pollution in China. In response, the Chinese government has implemented the most stringent livestock and poultry environmental regulations (LERs) in its history. Using a staggered DDD model and a manually collected panel dataset covering 1028 counties across ten provinces, this study examines the effects of LERs on hog production and water pollution pressure in boundary counties. The findings show that LER implementation increased slaughter volume and slaughter density in boundary counties by 8.68% and 11.42%, respectively, with stronger effects in economically less-developed regions, consistent with the “pollution haven” hypothesis. The effects of LERs exhibit significant heterogeneity across different hog-farming functional areas, with notable increases in hog production in boundary counties located in potential growth and constrained development areas. The increase in hog-farming intensity in boundary areas is associated with modest increases in selected water-pollution indicators. Specifically, LERs weaken the positive relationship between hog production and water pollution to some extent, but the relative expansion of hog production in boundary areas following LER implementation remains associated with additional pollution pressure. After accounting for the mitigating effect of LERs, the marginal effects of slaughter volume on COD Mn are 0.0672, and the marginal effects of slaughter density on COD Mn and NH₃-N are 0.0916 and 0.0755, respectively. The findings offer policy-relevant insights for improving the effectiveness of environmental regulation and addressing boundary-pollution issues.