Immunological response of Biomphalaria straminea (Gastropoda, Pulmonata) exposed to water pollution from an urban lake

PAREDES, M. G.; MARTINI, C.; MENÉNDEZ-HELMAN, R.; KRISTOFF, G.

Montevideo

Congreso; SETAC Latin America 15th Biennal Meeting; 2023

Lugano Lake is located in an Ecological Reserve of Buenos Aires City, Argentina. The water comes from rainfall and surface runoff, however, has been receiving raw sewage for a long period. Its study is essential due to the functions it performs, as a space for recreational and educational activities, and as a refuge for biodiversity. Biomphalaria straminea is a native hermaphroditic aquatic gastropod inhabiting freshwater bodies in Argentina. The immune defense of gastropods is simple, being the circulating hemocytes that can recognize foreign bodies, perform encapsulation responses, phagocytosis, and cytotoxic reactions. Thus, immunological responses have been proposed as biomarkers to environmental pollutants exposure. The aim of this work was to assess the viability and proportion of hemocytes population following a seven-day exposure to water samples from Lugano Lake (L1, L2, and L3) during four seasons over a year. Physicochemical parameters of the water samples were also analyzed. A control group was included, using tap water (TW). Dissolved oxygen varied seasonally (5.8 mgL-1 in summer to 20.2 mgL-1 in spring), conductivity was high which is usually indicative of contamination (max: 1741 μScm-1 in winter), and pH was persistently alkaline (8.5 - 10.4). Regarding nutrients, a concentration peak was observed for ammonium in winter (6.3 mgL-1) and phosphates in spring (8.7 mgL-1), while dissolved chemical oxygen (COD) ranged between 90 mgL-1 in winter to 504 mgL-1 in summer. Ammonium, pH, and COD exceeded aquatic life protection guidelines. Three types of hemocytes were identified: granulocytes, granulocytes with pseudopodia, and hyalinocytes. In autumn, spring, and summer, granulocytes and granulocytes with pseudopodia represented the higher % of the total hemocytes in snails exposed to L1, L2, and L3 with a maximum of 70% and 74%, respectively, while the % of hyalinocytes was lower. During winter, only organisms exposed to L2 showed a higher % of granulocytes (63%) and a lower % of hyalinocytes (31%). In TW, the hemocyte population comprised 55-71% hyalinocytes, 9-12% granulocytes, and 26-42% granulocytes with pseudopodia. No significant differences in non-viable hemocytes were recorded. Our results suggest that exposure to pollutants in the lake may compromise the immune system of B. straminea. This could be because granulocytes play a dominant role in the phagocytosis, while hyalinocytes are primarily involved in early inflammatory responses.