Accumulation Of Metals and Metalloids in Sediment and Aquatic Organisms of Ecuadorian Mangrove Forests and Implications for Human Health

Abstract

This study aims to determine the levels of toxic metals and metalloids and their ecotoxicological implications in two protected mangrove forests in Guayaquil, Ecuador: the Reserva de Producción Faunística Manglares El Salado (RPFMS) and the Refugio de Vida Silvestre Manglares El Morro (REVISMEM). Anthropogenic activities such as agriculture, urban development, and aquaculture introduce contaminants to these coastal forests, posing a risk to the ecosystems. We utilized inductively coupled plasma-mass spectrometry (ICP-MS) to quantify toxic elements. In Chapter 1, we examined concentrations of toxic metal(loid)s in sediment, catfish (Bagre pinnimaculatus), Peruvian mojarra (Diapterus peruvianus), and mussels (Mytella guyanensis, Mytella strigata, and Mytella trautwineana). In addition, we conducted dietary intake surveys with residents of Puerto Hondo in RPFMS to assess potential exposure through a quantitative health risk assessment. Our analysis revealed that concentrations of Ag, As, Cd, Cr, and Pb in sediment samples exceeded the US National Oceanic and Atmospheric Administration (NOAA) “effects range low” (ERL) guidelines, while Cu, Hg, Ni, and Zn exceeded their “effects range median” (ERM) guidelines. ERL and ERM represent the concentrations above which adverse effects may begin to occur and at which effects are frequently observed, respectively. In fish samples, iAs, Cd, MeHg and Se levels surpassed the US Environmental Protection Agency (EPA) screening levels for unlimited fish consumption with higher concentrations observed in catfish for most samples. For mussel samples (M. trautwineana), only Zn levels exceeded the guidelines of the Food and Agriculture Administration of the United Nations (FAO). The estimated daily intake (EDI) values for inorganic As (iAs), hexavalent chromium (Cr(VI)), methylmercury (MeHg) and Pb were higher in Peruvian mojarra compared to catfish. The target hazard quotient (THQ) and the hazard index (HI) did not exceed the threshold value of 1 in both fish species and mussels. Cancer Risk (CR) values indicated a potential carcinogenic risk from iAs and Cr(VI) in Peruvian mojarra, and from iAs in catfish and mussels. For Pb, the margin of exposure (MOE) values were in the safety threshold area, concluding that there are no potential exposure risks for both children and adults. In Chapter 2, we compared concentrations of toxic metal(loid)s in sediment and mussels (M. strigata) between RPFMS and REVISMEM. We found that As, Cr and Cu exceeded the ERL and Ni exceeded the ERM for sediment in both reserves, with higher concentrations in RPFMS. Most metal(loid) showed significant differences between “within city limits” (RPFMS) and “city border area” (RPFMS), “near the city” (REVISMEM) and “far from the city” (REVISMEM). For mussels, all the elemental concentrations were below the FAO threshold values for M. strigata. With the exception of As, Cd, and Co, all toxic elements showed higher concentrations in “near the city” (REVISMEM) compared to the “city border area” (RPFMS). This project aims to enhance understanding of the ecological effects of pollutants on these mangrove ecosystems, providing a scientific basis to prioritize conservation efforts and inform public policy actions. Collectively, our results show that RPFMS has more polluted sites than REVISMEM, with higher levels of toxic metal(loid)s in sediments, fish, and mussels. iAs in both mussels and fish and Cr(VI) only in Peruvian mojarra present carcinogenic risks. Pb in fish and mussel species do not pose a health risk. Catfish and Peruvian mojarra exhibit a HI lower than 1, indicating that non-carcinogenic health risks are unlikely for the Puerto Hondo community.