Short-Term Trace Element Distribution Following Application of Sargassum-Based Liquid Biofertilizer in a Soil–Plant–Tomato Fruit System

The recurrent influx of pelagic <i>Sargassum</i> spp. along Caribbean coastlines poses a significant environmental challenge while offering potential as a resource-recovery agricultural input. However, agricultural reuse of <i>Sargassum</i> biomass raises concerns regarding salinity and trace-metal distribution within the soil-plant-food continuum. This study evaluated the short-term elemental response to a <i>Sargassum</i>-Based Liquid Biofertilizer (SBLB) produced via controlled anaerobic fermentation, using tomato (<i>Solanum lycopersicum</i> L.) grown under greenhouse conditions. Raw biomass, fermented biofertilizer, irrigation water, soils, vegetative tissues, and fruits were chemically characterized. Elemental concentrations were quantified by ICP-OES and ICP-MS and treatment effects were analyzed using one-way and two-way ANOVA (<i>p</i> < 0.05). Anaerobic fermentation resulted in lower measured concentrations of sodium, arsenic, and selected trace elements in the liquid fraction relative to raw biomass. SBLB application increased soil macronutrient availability (N, P, K, Ca, Mg), while soil trace-metal concentrations remained within international reference ranges during the experimental period. Metals of concern (As, Cd, Pb, Ni, Cr) showed no detectable short-term enrichment in soils, vegetative tissues, or fruits relative to controls. In tomato fruits, arsenic, cadmium, and lead were below the limit of quantification across all treatments. Within the experimental timeframe, SBLB application was not associated with detectable trace-element accumulation in the soil-plant system. Long-term field studies and detailed soil physicochemical characterization are required to evaluate cumulative effects under repeated applications.