Coastal areas with dense populations and concentrated urban development face ecological and environmental issues such as pollution from emerging contaminants, with a large number of land-based pollutants being transported to the ocean via the land–sea interaction zone. Pharmaceutical and personal care products (PPCPs), which are not easily degraded in groundwater, have bioaccumulative and chronic toxicity properties that pose a threat to the health of ecosystems in the land–sea interaction zone. Moreover, PPCPs in this zone may be transported to the ocean via submarine groundwater discharge and can thereby potentially harm coastal aquatic organisms and the marine environment. Therefore, given that the coastal zone is a key node for land–sea integration and a strategic location for the scientific coordination of development and protection, further attention to its pollution by PPCPs is urgently required. The purpose of this study was to explore the behavioral characteristics of PPCPs in groundwater bodies in the land–ocean interzone of South China. In total, 60 groundwater samples were collected from Tangjiawan Town in Zhuhai City in September 2021, October 2022, and March 2023, respectively. The samples and data were analyzed using experimental and mathematical statistical methods, respectively. The following results were found: 1) During the wet season (April–October), six types of PPCPs were detected in the study area: sulfamethoxazole, sulfamethazine, sulfadimidine, cimaterol, carbamazepine, and caffeine. During the dry season (November–March of the following year), five types of PPCPs were detected: sulfamethoxazole, sulfadimidine, carbamazepine, caffeine, and atrazine. The concentrations of sulfamethoxazole, sulfamethazine, carbamazepine, and caffeine exhibited significant seasonal variations (P < 0.05). The rainfall-facilitated leaching or dilution of PPCPs in groundwater was the main cause of the seasonal differences in PPCP mass concentration. 2) Caffeine was a potential PPCP pollutant that could be discharged into the sea. The spatial variation in caffeine showed a decreasing trend as it moved from upstream to downstream of the watershed, nearing the sea. The flux of caffeine from submarine groundwater discharge into the sea along the unit length of the Zhuhai coastline was estimated to be approximately 33.2 μg/d. 3) The quantification of tritium (³H) isotopes in the groundwater revealed that the values at most sampling points were below 2 TU, indicating that the age of the groundwater can reach approximately 30 years. This is due to the mixing effect of residual groundwater in the aquifer medium and precipitation recharge. Using ³H dating software, a preliminary analysis of the changes in carbamazepine and caffeine contents in the groundwater over the past three decades revealed that the concentration of carbamazepine exhibited a decreasing trend, whereas that of caffeine showed a fluctuating downward trend, which was significantly influenced by annual precipitation and generally followed the same variation trend as annual precipitation. The results of this study can help to inform strategies for the prevention and management of groundwater pollution in the South China land–ocean interzone and provide a theoretical basis for the protection and sustainable utilization of groundwater resources.