Lead Dynamics in Saline Aquaponics: Tissue Accumulation in Litopenaeus vannamei and Sesuvium portulacastrum and Root-Associated Bacterial Communities

Lead (Pb) contamination in coastal groundwater poses a potential concern for aquaculture systems relying on saline water sources; however, biological patterns associated with naturally Pb-enriched water in integrated saline aquaponic systems remain poorly characterized. This exploratory study described Pb dynamics, plant tissue accumulation, shrimp physiological biomarkers, and root-associated microbiota in a single saline aquaponic system supplied with naturally Pb-enriched seawater (3.01 ± 1.03 µg/L) over eight weeks. Dissolved Pb concentrations were 75 ± 20% lower at the hydroponic outlet than at the sampled inlet, indicating system-level Pb retention. Pb accumulation in Sesuvium portulacastrum tissues indicates plant participation in Pb retention; however, the specific contribution of the plant could not be separated from retention by sedimentation, biofilter media, surfaces, or biofilms. Litopenaeus vannamei concentrated Pb predominantly in the cephalothorax and exhibited temporal fluctuations in hemocyte counts, osmolality, lysozyme activity, and catalase activity. Root-associated bacterial communities of aquaponic plants showed slightly higher genus richness (116 genera, H′ = 4.24) than dune reference plants (106 genera, H′ = 4.00), together with compositional differences involving saline- and metal-associated taxa. Because the study was based on a single aquaponic system without an uncontaminated parallel system or independent system-level replication, the observed patterns describe within-system temporal variation and cannot be attributed specifically to Pb. Nevertheless, the study illustrates the value of integrating plant, shrimp, and microbial indicators to characterize metal dynamics in saline aquaponic systems and provides exploratory evidence to guide future replicated studies of phytotechnology applications in contaminated coastal settings.