Does Sargassum spp. Compost Impact the Arsenic and Bacteria Levels within the Beach Environment?
Full-proposal Submitted to the HCSHWM on
April 12, 2023
PRINCIPAL INVESTIGATOR: Dr. Helena Solo-Gabriele
AFFILIATION: University of Miami, Dept. of Chemical, Environmental, and Materials Engineering
CONTACT INFORMATION: hmsolo@miami.edu, 305-284-3467
POST-GRADUATE STUDENT: Afeefa Abdool-Ghany
AFFILIATION: University of Miami, Dept. of Chemical, Environmental, and Materials Engineering CONTACT INFORMATION: aaa625@miami.edu, 954-298-4073
ABSTRACT
Sargassum, a floating macroalgae species known by scientific names of Sargassum natans and Sargassum fluitans, has been inundating the beaches across Florida in recent years during spring and summer months. These inundations are considered the “new normal” and their volumes are expected to increase in the future due to global climatologic factors which has been contributing to Sargassum blooms in the Atlantic Ocean. Typically, during large strandings events, municipalities hire third party contractors to haul away the Sargassum to a landfill, which is very costly. Once in the landfill, the Sargassum begins to rot and can release hydrogen sulfide. There is a need for municipalities to address these inundations in a sustainable way. Prior research has shown that limitations to the reuse of Sargassum include arsenic concentrations in excess of some regulatory guidelines and bacteria which also occasionally fail standards depending upon how the Sargassum is processed. For example, recent studies have documented that when Sargassum is composted the arsenic levels (6.64 to 26.5 mg/kg), exceed Florida Soil Cleanup Target Level guidelines, which limits the end use of the Sargassum compost. Similarly, Sargassum compost made using tumbler systems exceeded regulatory levels for fecal indicator bacteria, enterococci and fecal coliform.
One potentially viable option for the reuse of Sargassum is composting locally by setting up staging areas within the beach property, without the need to haul the Sargassum large distances. This compost can then be given away or used locally for dune or mangrove restoration. But excessive levels of arsenic and bacteria continue to be a concern for this potential reuse option. Regulators now raise questions about the background levels of arsenic at the beach and if Sargassum contributes towards excessive arsenic levels at beaches. Another question that arises is, “Will the Sargassum compost increase the arsenic burden at the beach if composted near or on the beach?” To answer these questions (which impact the reuse options for Sargassum) we aim to evaluate the background levels of arsenic and bacteria at beaches with various levels of Sargassum impacts coupled with laboratory experiments to simulate the fate of the arsenic and bacteria from Sargassum compost at the beach. The study is split into two phases. The first phase focuses on evaluating natural beach environments that are known for little to no accumulation of Sargassum, moderate accumulations, and hotspots for massive Sargassum inundations. Samples from the beach sites (Sargassum, sand below Sargassum, and beach water) will be analyzed for arsenic and the fecal indicator bacteria (FIB), enterococci. The second phase of the study will focus on controlled laboratory experiments that will examine the arsenic and fecal indicator bacteria levels in sand and Sargassum as it decomposes and is exposed to simulated rain. Assessing the background levels of arsenic and bacteria in the beach environment will allow for a better assessment of its reuse potential. The results of this study will contribute towards sustainable solutions that avoid the need for landfilling the potentially valuable Sargassum resource.