Surficial redistribution of fallout¹³¹iodine in a small temperate catchment

Abstract

Isotopes of iodine play significant environmental roles, including a limiting micronutrient ( 127 I), an acute radiotoxin ( 131 I), and a geochemical tracer ( 129 I). But the cycling of iodine through terrestrial ecosystems is poorly understood, due to its complex environmental chemistry and low natural abundance. To better understand iodine transport and fate in a terrestrial ecosystem, we traced fallout 131 iodine throughout a small temperate catchment following contamination by the 11 March 2011 failure of the Fukushima Daiichi nuclear power facility. We find that radioiodine fallout is actively and efficiently scavenged by the soil system, where it is continuously focused to surface soils over a period of weeks following deposition. Mobilization of historic (pre-Fukushima) 137 cesium observed concurrently in these soils suggests that the focusing of iodine to surface soils may be biologically mediated. Atmospherically deposited iodine is subsequently redistributed from the soil system via fluvial processes in a manner analogous to that of the particle-reactive tracer 7 beryllium, a consequence of the radionuclides’ shared sorption affinity for fine, particulate organic matter. These processes of surficial redistribution create iodine hotspots in the terrestrial environment where fine, particulate organic matter accumulates, and in this manner regulate the delivery of iodine nutrients and toxins alike from small catchments to larger river systems, lakes and estuaries.

Quantitative Retention of Atmospherically Deposited Elements by Native Vegetation Is Traced by the Fallout Radionuclides 7Be and 210Pb

“…However, this is a minimum and approximate estimate as it assumes all leaf areas are projected orthogonal to rain direction and that no rain shadow is cast by nearby branches or tree crowns. By comparison, a full canopy cumulatively retains on the order of 40−90% of depositional flux as estimated either by the fraction of standing inventory found in vegetation 51,17,18 or from comparisons of precipitation Each unique accumulative atmospheric ratio history begins with the leaf-out date of the tree and is shown as a shaded 1-sigma confidence interval. For clarity, error bars on leaf symbols for oak (circle, ○) and for hemlock (square, □ ) depict larger 2-sigma propagated uncertainty.…”

Joint isotopic mass balance: a novel approach to quantifying channel bed to channel margins sediment transfer during storm events

“…The transport and fate of radionuclide-tagged particles are controlled by the dynamics of fine-grained sediment transport in fluvial systems. Field observations have shown that finegrained sediment and atmospherically-deposited contaminants tend to accumulate in higher concentrations in channel margins that have been termed 'fine-grained channel margin' (FGCM) deposits (Skalak and Pizzuto, 2010;Landis et al, 2012a;Renshaw et al, 2013). However, the evolution of these deposits, such as the conditions under which they form and those under which they are eroded away, is not well established.…”

“…The different sources of suspended sediment can be identified and quantified because of their different characteristic radionuclide activities. The activity of precipitation is expected to be greatest while sediment stored on the channel bed is expected to have a lower 7 Be activity than the channel margin deposits due to the relatively long (with respect to 7 Be's half-life) residence time on the streambed (Bonniwell et al, 1999;Landis et al, 2012a).…”

“…If channel sediments are subsequently deposited onto the channel margins, the inventory of 7 Be activity of surface sediments increases, particularly near the channel's edge where deposition is greatest. This behavior is similar to many atmospherically deposited metals (Hawley et al ., ; Landis et al ., ; Renshaw et al ., ) and therefore 7 Be can be utilized as an effective tracer of particle‐reactive atmospheric contaminants. Field studies have confirmed this idea, demonstrating that 7 Be activity in sediment correlates with other atmospherically deposited metals, particularly in channel proximal areas (Landis et al ., ; Renshaw et al ., ).…”

Fukushima Daiichi–Derived Radionuclides in the Ocean: Transport, Fate, and Impacts

“…Following the CNPP accident in 1986, the concentrations of fission products such as 131 I, 137 Cs, and 90 Sr in foodstuffs in Ukraine were more than 1,000 times the baseline fallout concentrations (Nesterenko et al 2010). As with observations of fallout, once these and other anthropogenic radionuclides were released into the environment, their activities steadily decreased owing to a combination of radioactive decay and biological and geochemical redistributions (e.g., Landis et al 2012).…”