Radioiodine Biogeochemistry and Prevalence in Groundwater

Figures & data

FIGURE 1. Relative total activity emitted as a function of time after the Chernobyl accident. Note that ¹³¹I accounted for much of the radiation during the first week (redrawn from IAEA, 2006).

TABLE 1. Inventory of radioiodine isotopes produced in a representative material irradiated by a production reactor (Kantelo et al., 1990)

		Curies remaining at various times after irradiation
Isotope	Half-life	0 s	24 hr	100 days	200 days
128	25 minutes	1.5 × 10^4	—	—	—
129	1.6 × 10^7 years	2.3 × 10^−1	2.3 × 10^−1	2.5 × 10^−1	2.5 × 10^−1
130m	9 minutes	9.2 × 10^4	—	—	—
130	12 hr	1.4 × 10^5	3.5 × 10^4	—	—
131	8.0 days	7.6 × 10^7	7.0 × 10^7	1.3 × 10^4	2.3 × 10^0
132	2.3h/3.3 days **	1.1 × 10^6	8.9 × 10^7	—	—
133 g	9 s	3.8 × 10^6	—	—	—
133	21 hr	1.8 × 10^4	8.2 × 10^7	—	—
134 m	4 minutes	1.3 × 10^7	—	—	—
134	53 minutes	2.0 × 10^8	1.3 × 10^8	—	—
135	6.6 hr	1.6 × 10^8	1.5 × 10^7	—	—
136 m	47 s	5.0 × 10^7	—	—	—
136	83 s	7.9 × 10^7	—	—	—
137	24 s	7.9 × 10^7	—	—	—
138	7 s	4.1 × 10^7	—	—	—
139	2 s	1.8 × 10^7	—	—	—
140	<1 s	4.1 × 10^6	—	—	—
141	<1 s	8.6 × 10^5	—	—	—
142	<1 s	1.1 × 10^5	—	—	—
Totals		1.0 × 10^9	2.6 × 10^8	1.3 × 10^4	2.5 × 10^0

These calculations demonstrate that radioiodine total activity decreases rapidly and after 100 days, only ¹²⁹I and ¹³¹I are present.

TABLE 2. Radiochemical properties of ¹²⁹I and ¹³¹I

	^129I	^131I
Half life	1.6 × 10^7 years	8.0197 days
Neutrons	77	78
Protons	52	53
Radiation	ß 0.154 keV (100%);	ß 0.606 (90%) keV;
	γ 0.0396 (7.5%), γ 0.0295 (20%)	γ 0.364 (82%)
Decay	^12953I → β + ^12954Xe	^13153I → β + ^13154Xe
Fission yield^a	0.6576% per fission ^235U	2.8336% per fission ^235U

^aNuclear fission splits a heavy nucleus such as uranium or plutonium into two lighter nuclei, which are called fission products. Yield refers to the fraction of a fission product produced per fission.

TABLE 3. Major sources of ¹²⁹I in the environment (compiled from Raisbeck and Yiou, 1999)

Source	^129I (kg)
Atmospheric testing	50
Chernobyl	1–2
Savannah River Site	32^a
Hanford Reservation	266
Nevada Test Site underground nuclear testing	10
Yucca Mountain repository	13,300
Fuel reprocessing Sellafield (UK)	1640
Fuel reprocessing at La Hague (France)	720
Natural hydrosphere and atmosphere	100^b

^aKantelo et al. (1990).^bNCRP (1983).

FIGURE 2. ¹²⁹I plumes in the surface aquifer of the 200 East and 200 West Areas on the Hanford Site. 129I plumes coexist with other contaminants. ¹²⁹I, ⁹⁹Tc, and ³H are the primary risk drivers at the site (Department of Energy, 2012b).

FIGURE 3. Groundwater plume map in the 200 West Area (including 200-UP-1 and 200-ZP-1 Operable Units). The plumes primarily emanate from disposal cribs located near U Plant and S Plant (Department of Energy, 2012b).

FIGURE 4. ¹²⁹I plume map of F-Area, H-Area, and Burial Ground (BG) plumes on the Savannah River Site; green lines are contours of water table potentiometric surface, blue dots with numbers are monitoring wells.

TABLE 4. Reactions of log K association constants of selected aqueous species of iodine

Reaction	log K20°C
I^− + H^+ = HI	0
2I^− = I2(aq) + 2e^−	−21.33
3I^− = I3^− + 2e^−	−18.44
I^− + H2O = HIO(aq) + H^+ + 2e^−	−33.81
I^− + H2O = IO^− + 2H^+ + 2e^−	−44.53
I^− + 2e^− = I^−3	−0.90
I^− + 3H2O = HIO3(aq) + 5H^+ + 6e^−	−112.56
I^− + 3H2O = IO3^− + 6H^+ + 6e^−	−113.31
I^− + 4H2O = IO4^− + 8H^+ + 8e^−	−168.10

FIGURE 5. Solubility of various metal iodides expressed as the aqueous metal concentration (log mol/L) at 10 μg/L iodide.

FIGURE 6. Eh-pH diagram of aqueous iodine speciation; solid line = total iodine concentration of 1 μg/L, a typical groundwater concentration, dotted line = total iodine concentration of 58 μg/L, a typical seawater concentration (Fuge and Johnson, 1986); dashed lines are stability limits of water (note that organo-iodine species are not included in these calculations).

TABLE 5. Stable ¹²⁷I and radioactive ¹²⁹I speciation in groundwater collected in March 2012 from 200 West Area (Santschi et al., 2012)

		^127I				^129I
	TOC	Total	Iodide	Iodate	Organo-I	Total	Iodide	Iodate	Organo-I
	μM	μM	μM (%)	μM (%)	μM (%)	(pCi/L)	(pCi/L)	(pCi/L)	(pCi/L)
299-W14–11	50.2	0.79	0.015 (2%)	0.707 (90%)	0.066 (8%)	31.6	<2	31.6	<5
299-W14–13	63.0	0.58	0.012 (2%)	0.481 (84%)	0.084 (14%)	35.6	<2	35.6	<5
299-W1–88	15.6	0.14	0.002 (2%)	0.141 (98%)	<0.003 (0%)	6.63	<2	6.63	<5

TABLE 6. Iodide and iodate K_d values after 21 days of composite sediments recovered from 200 West Area borehole cores (Santschi et al., 2012)

Composite sediment^a	Organic carbon (%)	Inorganic carbon (%)	Total sediment iodine (μg/g)	Total DOC (μM)^b	Iodide, spiked Kd (mL/g)^c	Iodate spiked Kd (mL/g)^c
H3	0.15	0.18	2.10	94 ± 17	3.38	3.94
H1	0.12	0.92	4.79	284 ± 33	0.08	1.78
H2	0.04	0.01	0.68	0	0.00	0.83

^aSediment 1: composite of fine-grained sediments, mostly silt, from the vadose zone of borehole cores 299-W11–92 and 299-W15–226. Natural calcium carbonate cementation of the sediment was apparent. Sediment 2: composite from different depths within one well (299-W11–92). Sediment 3: composite of saturated zone sediments of two different wells: 299-W11–92 and 299-W15–226.^bTotal dissolved organic carbon is the total organic carbon released from the sediment to the aqueous phase (<0.45 μm) after 21 days of contact during the sediment/groundwater batch iodine uptake experiment.^cSuspensions were spiked with either iodide or iodate but during contact period the spiked species transformed to other species. Consequently these are not species-specific K_d values.

FIGURE 7. Biological transformations of iodine (Amachi et al., 2005a).

FIGURE 8. Iodide surrounded by (A) Aqueous hydration shell; (B) intracellular phenols, carbohydrates, or amines (Küpper et al., 2008).

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