Date of Award

Summer 2019

Project Type

Thesis

Program or Major

Biological Sciences

Degree Name

Master of Science

First Advisor

James Haney

Second Advisor

Alan Baker

Third Advisor

Inga Sidor

Abstract

Cyanobacteria produce a range of toxins harmful to both humans and wildlife. Microcystins (MCs) are common and potent cyanotoxins that inhibit protein phosphatases in the liver. Chronic exposures can result in tumor promotion and cancer. Toxicity primarily follows ingestion of MCs, however inhalation may be an important secondary and compounding route of exposure to cyanotoxins. The LD50 of intratracheally applied MC-LR is 50x lower than the oral LD50. While MCs are well documented in water, little is known about cyanobacteria and cyanotoxins in aerosols and the factors that regulate the movement of cells and toxins into the air. To begin characterizing cyanobacteria presence in the air, lake-generated aerosols were measured from eight New England lakes of varying productivity. Air samples were collected with a portable on-lake aerosol monitor for nine-hour periods during the day, and nine-hour periods directly following day sampling at night. Corresponding water samples were taken at the beginning and end of each aerosol sampling period. Environmental and water quality factors were collected simultaneously with aerosols.

In this first study documenting MCs aerosols generated from low-productivity lakes, microcystin concentrations ranged from below detectable levels to 3.79 pg MCs m-3 from lakes with a range of 4 to 90 ng MCs L-1 in the near surface lake water. The presence of MCs in aerosols from low productivity lakes demonstrates the wide prevalence of aerosolized cyanobacteria. A combination of techniques, including sample concentration and the use of epifluorescence, were employed to quantify low levels of toxins and cyanobacteria cells in the aerosols. Aerosolized MCs were correlated with total aerosolized cells at night (p = 0.008, Adj R2: 0.66), but not during the day, potentially indicating differences in aerosolization mechanisms and drivers based on time of day. Total aerosolized cyanobacteria ranged from 3.5×104 to 1.9×105 cells m-3. On average, 56.9 ± 4.23% of total cells are picocyanobacteria (0.22 – 2 µm), and 99.2 ± 0.14% of cells were smaller than 10 µm. Emission of larger cells (>2 – 40 µm) varied based on the lake. No colonies were detected in aerosols.

The community composition of cyanobacteria in lake water has an influence on the aerosol cell and toxin composition as not all cyanobacteria are equally as likely to become aerosolized (as seen by the dominance of small cells in aerosols). Despite nine times higher MCs toxicity in the large net cyanobacteria compared to all other sampled lakes, Lake Attitash did not emit significantly higher levels of aerosolized MCs. Lower productivity lakes with low water MCs had disproportionately higher aerosolized toxins and cyanobacteria cells (power function linear regression, p <0.0001, Adj R2: 0.85). A probable explanation is that low MCs lakes are dominated by small cyanobacteria that produce low levels of toxin but are more likely to enter the air, while high MCs lakes are dominated by large colonial forms that are more likely to remain in the water.

At night, cyanobacteria cells became aerosolized in more predictable patterns than during the day. Though the time of day effect on aerosolization varied between lakes, aerosolized cell concentrations were more strongly correlated with environmental factors at night across all lakes. Toxicity in the water and the temperature differential between the air and water were the two most important environmental drivers of cyanobacteria cell aerosolization. Wind was surprisingly negatively correlated to total and larger cells (both parameters log10 transformed: total cells p = 0.033, Adj R2: 0.235; larger cells p = 0.015, Adj R2: 0.306). Although the human health effects of MCs in aerosols have not been defined, the levels of both cyanobacteria cells and microcystins described in this study suggest possible chronic effects on humans and wildlife. The dominance of picocyanobacteria also indicates the potential for cells to travel deep into lung tissue. Building an understanding of aerosolized MCs and the sizes of aerosolized cyanobacteria cells emitted from varying lake types, and the factors regulating this process, could lead to better estimates of cyanotoxin exposure.

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