MS in Environmental Engr. (M.S.E.V.)
Degree Granting Department
Civil and Environmental Engineering
Maya Trotz, Ph.D.
James Mihelcic, Ph.D.
Rebecca Zarger, Ph.D.
eucheuma isiforme, exposure dose, mariculture, Placencia, sustainable livelihoods
Certain macroalgae, commonly referred to as seaweed, have traditionally been used as a food source for many coastal communities around the world. In Belize, residents of the Placencia Peninsula cultivate two seaweed types, Eucheuma isiforme and Gracilaria spp. at Little Water Caye located 19 miles offshore. The dried seaweed is sold at the Placencia Producers Cooperative Society Limited (PPCSL) where community members process it into a variety of value-added products such as soaps, cosmetics, hair products, and food additives.
The overall goal of this research was to understand the existing food-energy-water system (FEWS) infrastructure landscape for seaweed production in Placencia, Belize, and identify environmental engineering intersections for future research. Two research questions guide this research: 1) How are FEWS interconnected in the seaweed production process in Placencia, Belize? and 2) Does the ingestion of Eucheuma isiforme sold in Placencia, Belize pose a health risk threat from exposure to heavy metals?
In answering research question 1, semi-structured interviews and informal interviews were conducted with five stakeholders involved in the seaweed farming endeavor to contextualize the current culture of seaweed farming, and implications on food-energy-water systems in Placencia, Belize. Literature on cultivation approaches, seaweed species’ biochemical and physical properties, national and international partners, and previous research in Placencia were also collected to determine differences in technology across various landscapes, and to identify support networks. An additional two informal conversations were held with The Nature Conservancy Belize (TNC) and a private seaweed production enterprise on topics related to seaweed farming. These interviews, literature review, and field observations completed between June 1st and June 15th, 2020, were all used to highlight relationships among key variables in the seaweed farming system and construct a Causal Loop Diagram (CLD) using a systems thinking approach.
To address research question 2, a heavy metal analysis and health risk assessment were conducted. Three samples of Eucheuma isiforme originating from Little Water Caye were collected in dried form and analyzed. The samples were labeled EVAP_Raw for raw dried seaweed samples rinsed by evaporation, RWH_Raw for raw dried seaweed samples rinsed by collected rainwater, and RRWH_VAP for the value-added product that was made from seaweed rinsed by rainwater. Samples were analyzed by ICP-MS. Average concentrations found by the heavy metal analysis were used for calculating exposure dose, targeted hazard quotients (THQ), and the hazard index (HI) of consuming Eucheuma isiforme for a 70 kg adult and 10 kg child.
The CLD showed that water and energy in this system are closely connected. Seaweed farming is freshwater and energy intensive, requiring approximately 192 gallons (726.8 L) of freshwater to rinse roughly 75 lbs (34 kg) of dried seaweed (8 lbs of wet seaweed = 1 lb of dried seaweed) and about $300 BZ ($150 USD) for fuel. During the rainy season, rainwater is collected using a rainwater harvesting system that was constructed on the island. At times during the dry season, freshwater is shipped from Placencia. Seaweed farmers find that processing of the seaweed from cultivation, to harvesting, rinsing, and drying on the island requires less expenses than if they were to transport the seaweed in its wet stage to the mainland. Awareness of seaweed’s nutritional benefits is growing throughout Belize. It is being used as a substitute for pectin and gelatin, contributing to local food supply and stimulating the local economy. With this promotion, demands for energy and water increase as well. Intersections with environmental engineering and hence leverage points from this include addressing freshwater provisioning through rainwater harvesting system characterization, assessing biofuel potential from Eucheuma isiforme used to manage nitrogen from onsite wastewater systems, and designing a “seaweed hub.”
Given the human consumption of Eucheuma isiforme in Belize it is important to have information on the safety of these products from a health perspective. While seaweed is known to contain many essential minerals, it can also accumulate toxic metals. The loadings as μg/g of chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), selenium (Se), cadmium (Cd), mercury (Hg), and lead (Pb) on dried Euchema Isiforme purchased or obtained in Placencia, Belize were measured. With the exception of Cr, Se, Pb, and Hg, the recovery rate of these elements in NIST standards of apple and spinach leaves, were between 70 and 80%. Recovery rates of Cr were 98%, whereas Se, Pb, and Hg, had differences greater than 50%. Zinc loadings were highest in all three seaweed samples tested. Levels of Zn for the EVAP_Raw samples were found to be 4.21 ± 0.032 μg/g while RWH_Raw and RWH_VAP were 10.28 ± 2.36 and 9.19 ± 0.030 μg/g, respectively. This same behavior is also seen with Cu where values in EVAP_Raw was lower at 0.675 ± 0.031 μg/g while Cu concentrations in RWH_Raw and RWH_VAP were 0.970 ± 0.037 and 0.716 ± 0.005 μg/g, respectively. Cr concentrations were 1.24 ± 0.492 μg/g for EVAP_Raw, 1.59 ± 0.067 μg/g for RWH_Raw, 0.918 ± 0.097 μg/g for RWH_VAP. Ni concentrations were 0.776 ± 0.307 μg/g for EVAP_Raw, 0.861 ± 0.046 μg/g for RWH_Raw, and 0.535 ± 0.174 μg/g for RWH_VAP. As concentrations were 3.87 ± 0.071 μg/g for EVAP_Raw, 3.97 ± 0.179 μg/g for RWH_Raw, and 4.49 ± 0.003 μg/g for RWH_VAP. Se concentrations were 0.371 ± 0.067 μg/g for EVAP_Raw, 0.363 ± 0.041 μg/g for RWH_Raw, and 0.637 ± 0.168 μg/g for RWH_VAP. Cd concentrations were 0.386 ± 0.007 μg/g for EVAP_Raw, 0.350 ± 0.008 μg/g for RWH_Raw, and 0.314 ± 0.004 μg/g for RWH_VAP.
The health risk assessment found a hazard index (HI) of less than 1 for an ingestion rate of 3080 mg/day (assumed weight of seaweed in gelatinous form), indicating the intoxication of consuming Eucheuma isiforme is minimal. At 30% higher concentrations of heavy metals, the HI value for a 70 kg adult and 10 kg child were still under 1 indicating a low health risk. At 30% higher concentrations and an ingestion rate of 5000 mg/day, the HI value for a 70 kg adult was below 1 indicating a low health risk. However, the HI value for a 10 kg child was above 1 indicating a potential health risk from consuming Eucheuma isiforme for this age group. Future research is needed to address onsite water and wastewater quality for heavy metals sources and microbial contamination. In addition to this, future research can also address the intersections with environmental engineering from either a perspective to remove the heavy metals for consumption or to remove heavy metals as a treatment process for other types of value add products .
Scholar Commons Citation
Ortiz Carabantes, Estenia J., "Using a Systems Thinking Approach and Health Risk Assessment to Analyze the Food-Energy-Water System Nexus of Seaweed Farming in Belize" (2020). USF Tampa Graduate Theses and Dissertations.