Sources, Levels, and Reactions of Boron in Florida Waters

Abstract

Levels of boron in Florida natural waters are generally low, (median value <50 µg/liter for 120 samples) and not of toxic concern. However, municipal sewage effluents have levels high enough (150–800 µg/liter) to cause phytotoxicity, at least to sensitive plants such as citrus. Detergent use of borate softeners and perborate bleaches is evidently the source of the elevated boron levels in sewage. Boron concentrations in rainfall increase with proximity to either coast in peninsular Florida, reaching levels of 80–90 µg/liter. Marine aerosols are thus implicated as an important natural source in the boron cycle of Florida. Model ecosystem studies indicated little bioaccumulation and no toxic hazard at levels expected in natural waters. Interactions of boron with clays and with dissolved organic color (humates) were found to be small, and boron behaves as an essentially conservative element in natural waters.

Transfer of atmospheric boron from the oceans to the continents: An investigation using precipitation waters and epiphytic lichens

“…Samples of this latter species from Asia (Nepal) have an even lower B concentration of 1 ppm, corresponding to a decrease of $83% at $700 km. Along the first 200 km away from the ocean, the magnitude of the decrease in B concentration for lichens and snowpacks is similar to that previously described for rains in different locations and ascribed to a decreasing marine influence inland [Carriker and Brezonik, 1978;Meybeck, 1984]. At variance with the systematic tendency shown by lichens and snowpacks, individual rain events (Asian rains sampled over Bangladesh and Nepal over a transect of 700 km) do not show a systematic B decrease with distance from the sea (Figure 3).…”

“…Despite systematic higher B concentrations observed in coastal areas for rains in Florida [ Carriker and Brezonik , 1978], no agreement exists as to whether the ocean is a sink or a source for B in the atmosphere. In addition, it was also shown that the partitioning of gaseous B between sea salts and the atmosphere was strongly dependent on temperature and pH, which controls B speciation [e.g., Duce , 1996].…”

“…The major fraction of the atmospheric B is gaseous, commonly considered to be essentially in the form of boric acid (B(OH) 3 ), with a gas to particulate ratio for B % 74 [Fogg and Duce, 1985]. [3] Though coastal rains may show B enrichments by a factor of 2 or more compared to rain sampled at distance from the sea [Carriker and Brezonik, 1978;Fogg and Duce, 1985] and are known to be enriched in B relative to seawater ((B/Na) rain /(B/Na) sea % 11 [Gast and Thompson, 1959;Fogg and Duce, 1985]), the role of the oceans either as a source or as a sink for atmospheric B is still debated. This is first due to the fact that coastal rains show a strong variability in B concentrations, i.e., from 0.3 to 12 ppb B at Narragansett, Rhode Island [Fogg and Duce, 1985].…”

Boron isotopic composition of atmospheric precipitations and liquid–vapour fractionations

“…2a) comes from aerosols gives a maximum contribution of 0.2%. Coastal rains in Florida with 75 ppb B could contain a maximum contribution of 1.7% seawater aerosol (Carriker and Brezonik, 1978). Partial water evaporation of seawater droplets before incorporation in rains adds a very small quantity of 11 B depleted vapour (initially $+14&) relative to seawater plus liquid or solid aerosols with d 11 B like that of seawater.…”