Heavy metals, including As, Cd, Cr, Cu, Ni, Pb, Zn, and Al, are persistent pollutants with severe consequences for human health and aquatic ecosystems. These pollutants enter aquatic environments through industrial activities, agriculture, and urban runoff, accumulating in organisms and posing significant risks to the food chain. Monitoring heavy metals (HMs) is challenging due to their bioavailability being influenced by site-specific abiotic factors such as pH, temperature, and organic matter content. In response, the Louisiana Department of Environmental Quality (LDEQ) is working to update aquatic life criteria (ALC) for these contaminants. Identifying natural passive samplers, such as freshwater sponges (FWS), could enhance the efficiency of assessing HMs threats to Louisiana’s ecosystems and communities.
FWS, which make up only 3% of global sponge species, are sessile filter feeders with an exceptional capacity to bioaccumulate contaminants, including HMs (Figure1), making them promising passive samplers. While laboratory studies have demonstrated toxicity at low HMs concentrations, sponges in natural conditions accumulate HMs in proportion to environmental pollution levels. In Southern Louisiana, sponges thrive under unique environmental conditions—high temperatures, elevated dissolved organic matter, and salinity—that differ from temperate regions previously studied. Given their year-round presence in Louisiana’s FW systems, sponges show significant potential for monitoring HMs pollution.
This study evaluates the feasibility of using freshwater sponges (FWS) as passive samplers by comparing heavy metal (HM) bioaccumulation in FWS tissues with concentrations in water and sediment samples. Samples were collected from Bayou St. John (BSJ) and Daniel Branch (DB) in southeastern Louisiana. HMs were analyzed using inductively coupled plasma mass spectrometry (ICP-MS), and the species of the collected FWS was confirmed via optical microscopy.
Heavy metal concentrations in water were significantly lower than those in both sediment and FWS samples. Water samples were within the safe limits defined by the World Health Organization (WHO) and U.S. Environmental Protection Agency (EPA) guidelines. However, sediment from BSJ showed elevated levels of As (1774.97 mg/kg), while Cr concentrations were notably higher in DB (27.82 mg/kg). Concentration of Al was (1772.28 mg/kg) in BSJ sediment and (19860.93 mg/kg) in DB sediment, and there is no EPA guidelines exist for Al in sediment concentrations.
Heavy metal bioaccumulation in FWS affects their spicule structure. Malformed spicules indicate higher metal adsorption, serving as a visible sign of water quality and pollution. This makes FWS a useful tool for monitoring aquatic environments.