Toxicity of MCHM: Supplementary materials
Supplementary Material: Daily Adult MCHM Exposure Assuming Typical Ingestion of
Contaminated Water After The Elk River Spill (even though there was a ‘do not use order’ and
presence of an odor)
A. Adult Oral Ingestion of MCHM in Tap Water
Adult oral exposure to MCHM was calculated based on the USEPA exposure factors used to derive
regional screening levels (USEPA 2014) as shown below. We evaluated three exposure scenarios. In the
first example, the tap water concentration of MCHM was assumed to be at the analytical detection limit of
0.01 ppm (10 µg/L). Second, we examined the CDC’s short-term health advisory of 1 ppm (1,000 µg/L).
Third, we examined the highest reported concentration in finished water of 3.1 ppm (3,100 µg/L).
𝐼𝑛𝑔𝑒𝑠𝑡𝑖𝑜𝑛𝑀𝐶𝐻𝑀 =
[(𝐶𝑤𝑎𝑡𝑒𝑟 )𝑥 (𝐶𝐹)𝑥 (𝐼)]
𝐵𝑊
Where:
IngestionMCHM: Ingestion of MCHM for an adult in tap water per day (mg/kg-day)
Cwater: Concentration of MCHM in tap water (10, 1,000 or 3,100 µg/L)
CF: Conversion factor (0.001 mg/µg)
I: Intake of water for an adult per day (2.5 L) (USEPA 2014) (Note: We used the EPA default
value of 2.5 L/day even though it is known that in the U.S. a large fraction of ingested fluid is not
tap water (e.g., canned beverages, bottled water). Also, many persons drink coffee, teas, or
otherwise heat/boil their water, which will reduce the concentration of the volatile contaminants.)
BW: Adult body weight (80 kg) (USEPA 2014)
Scenario I: Assuming the MCHM tap water concentration is at the detection limit (10 µg/L):
𝜇𝑔
0.001 𝑚𝑔
𝐿
[(10 𝐿 ) 𝑥 ( 𝜇𝑔 ) 𝑥 (2.5 𝑑𝑎𝑦)]
𝑚𝑔
= 0.00031
80 𝑘𝑔
𝑘𝑔 − 𝑑𝑎𝑦
1
Toxicity of MCHM: Supplementary materials
Scenario II: Assuming the MCHM tap water concentration is at the CDC short-term health advisory
(1000 µg/L):
𝜇𝑔
0.001 𝑚𝑔
𝐿
)]
[(1000 𝐿 ) 𝑥 ( 𝜇𝑔 ) 𝑥 (2.5
𝑚𝑔
𝑑𝑎𝑦
= 0.031
80 𝑘𝑔
𝑘𝑔 − 𝑑𝑎𝑦
Scenario III: Assuming the MCHM tap water concentration is at the highest concentration detected in
finished water (3,100 µg/L):
𝜇𝑔
0.001 𝑚𝑔
𝐿
[(3100 𝐿 ) 𝑥 ( 𝜇𝑔 ) 𝑥 (2.5 𝑑𝑎𝑦)]
𝑚𝑔
= 0.097
80 𝑘𝑔
𝑘𝑔 − 𝑑𝑎𝑦
B. Adult Dermal Contact with MCHM in Tap Water (Bathing)
Adult dermal uptake (absorption) of MCHM during water contact (bathing) was calculated based on the
USEPA RAGS part E (USEPA 2004) as shown below. Three scenarios were evaluated. The tap water
concentration of MCHM was assumed to be at (1) the analytical detection limit of 0.01 ppm (10 µg/L),
(2) the CDC’s short-term health advisory of 1 ppm (1,000 µg/L), (3) or the highest reported concentration
in finished water of 3.1 ppm (3,100 µg/L) (WVAW 2014b, 2014a). [Based on the short duration of skinwater contact, the reduced amount of skin surface area continually in contact with water (in comparison to
bathing), and the predicted octanol/water co-efficient, dermal uptake during showering would likely be
low or negligible.]
Predicted MCHM permeability coefficient:
log 𝐾𝑝 = −2.80 + 0.66 𝑥 log 𝐾𝑜𝑤 − 0.0056 𝑥 𝑀𝑊
𝐾𝑝 = 10(−2.8+0.66𝑥𝐾𝑜𝑤−0.0056𝑥𝑀𝑊)
Where:
Kp: Dermal permeability coefficient of MCHM in water (cm/hr)
Log Kow: Log Kow of MCHM as predicted by VEGA (average =2.22)
MW: Molecular weight of MCHM (128.2 g/mol)
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Toxicity of MCHM: Supplementary materials
0.0089𝑐𝑚/ℎ𝑟 = 10(−2.8+[0.66
𝑥 2.22]−[0.0056 𝑥 128.2])
Dermal MCHM exposure potential (called dermal absorbed dose per event by the EPA) for an adult
during bathing
6 𝜏𝑒𝑣𝑒𝑛𝑡 𝑥 𝑡𝑒𝑣𝑒𝑛𝑡
𝜋
𝐷𝐴𝑒𝑣𝑒𝑛𝑡 = 2 𝐹𝐴 𝑥 𝐾𝑝 𝑥 𝐶𝑤𝑎𝑡𝑒𝑟 √
Where:
DAevent: Dermal exposure potential or absorbed dermal dose per an bathing (mg/cm2-event)
FA: Fraction absorbed water (1 dimensionless)
Kp: Dermal permeability coefficient of MCHM in water (0.0089 cm/hr)
Cwater: Concentration of MCHM in tap water (10, 1,000 or 3,100 µg/L which is equivalent to
0.00001 mg/cm3, 0.001 mg/cm3, or 0.0031 mg/cm3)
τevent: Lag time per event (0.55 hr/event)
𝜏𝑒𝑣𝑒𝑛𝑡 = 0.105 𝑥 10(0.0056 𝑥 𝑀𝑊)
0.55 ℎ𝑟/𝑒𝑣𝑒𝑛𝑡 = 0.105 𝑥 10(0.0056 𝑥 128.2)
tevent: Assumed duration of bathing 17 min (0.28 hr/event) (USEPA 2011)
Scenario I: Assuming the MCHM tap water concentration is at the detection limit (10 µg/L= 0.00001
mg/cm3):
ℎ𝑟
ℎ𝑟
𝑐𝑚
𝑚𝑔 √6 𝑥 0.55 𝑒𝑣𝑒𝑛𝑡 𝑥 0.28 𝑒𝑣𝑒𝑛𝑡
𝑚𝑔
2 𝑥 1 𝑥 0.0089
𝑥 0.00001 3
= 9.65 𝑥10−8
ℎ𝑟
𝑐𝑚
𝜋
𝑐𝑚2
Scenario II: Assuming the MCHM tap water concentration is at the CDC short-term health advisory
(1000 µg/L = 0.001 mg/cm3):
ℎ𝑟
ℎ𝑟
𝑐𝑚
𝑚𝑔 √6 𝑥 0.55 𝑒𝑣𝑒𝑛𝑡 𝑥 0.28 𝑒𝑣𝑒𝑛𝑡
𝑚𝑔
2 𝑥 1 𝑥 0.0089
𝑥 0.001 3
= 9.65 𝑥10−6
ℎ𝑟
𝑐𝑚
𝜋
𝑐𝑚2
3
Toxicity of MCHM: Supplementary materials
Scenario III: Assuming the MCHM tap water concentration is at the highest concentration detected in
finished water (3,100 µg/L = 0.0031 mg/cm3):
ℎ𝑟
ℎ𝑟
𝑐𝑚
𝑚𝑔 √6 𝑥 0.55 𝑒𝑣𝑒𝑛𝑡 𝑥 0.28 𝑒𝑣𝑒𝑛𝑡
𝑚𝑔
2 𝑥 1 𝑥 0.0089
𝑥 0.0031 3
= 2.99 𝑥10−5
ℎ𝑟
𝑐𝑚
𝜋
𝑐𝑚2
Dermal MCHM dose during bathing
𝐷𝑒𝑟𝑚𝑎𝑙𝑀𝐶𝐻𝑀 =
[𝐷𝐴 𝑒𝑣𝑒𝑛𝑡 𝑥 𝑆𝑆𝐴 𝑥 𝐸𝐹]
𝐵𝑊
Where:
DermalMCHM: Dose for an adult during bathing (mg/kg-day)
DAevent: Dermal exposure potential or absorbed dermal dose per an event (mg/cm2-event)
SSA: Skin surface area for an adult (20,900 cm2) (USEPA, 2014)
EF: Exposure frequency (1 event/day)
BW: Adult body weight (80 kg) (USEPA, 2014)
Scenario I: Assuming the MCHM tap water concentration is at the detection limit:
[9.65 𝑥10−8
𝑚𝑔
𝑥 20,900𝑐𝑚2 𝑥 1 𝑒𝑣𝑒𝑛𝑡/𝑑𝑎𝑦]
𝑚𝑔
𝑐𝑚2
= 2.52 𝑥 10−5
80 𝑘𝑔
𝑘𝑔 − 𝑑𝑎𝑦
Scenario II: Assuming the MCHM tap water concentration is at the CDC short-term health advisory:
[9.65 𝑥10−6
𝑚𝑔
𝑥 20,900𝑐𝑚2 𝑥 1 𝑒𝑣𝑒𝑛𝑡/𝑑𝑎𝑦]
𝑚𝑔
𝑐𝑚2
= 2.52 𝑥 10−3
80 𝑘𝑔
𝑘𝑔 − 𝑑𝑎𝑦
4
Toxicity of MCHM: Supplementary materials
Scenario III: Assuming the MCHM tap water concentration is at the highest concentration detected in
finished water:
[2.99 𝑥10−5
𝑚𝑔
𝑥 20,900𝑐𝑚2 𝑥 1 𝑒𝑣𝑒𝑛𝑡/𝑑𝑎𝑦]
𝑚𝑔
𝑐𝑚2
= 7.81 𝑥 10−3
80 𝑘𝑔
𝑘𝑔 − 𝑑𝑎𝑦
C. Adult Inhalation of MCHM While Showering
Adult inhalation exposure to MCHM during showering was calculated based on USEPA (2014) as shown
below. The tap water concentration of MCHM was assumed to be at (1) the analytical detection limit of
0.01 ppm (10 µg/L), (2) the CDC’s short-term health advisory of 1 ppm (1,000 µg/L), or (3) the highest
reported concentration in finished water of 3.1 ppm (3,100 µg/L).
The air concentration during showering was estimated using a model of volatilization based on two film
resistance theory (Little 1992). This model was used to estimate a steady state volatilization factor (0.137
µg/m3 per µg/L) (time-weighted average; not steady state) that was used to estimate the air concentration
in bathroom air based on the concentration in shower water (1.37, 137, 424 µg/m3 for scenarios I, II, and
III, respectively). We also considered some empirical data (Kerger et al. 2000; Jo et al. 1990; McKone et
al. 1991). To calculate the estimated air concentration two-resistance theory was applied to the transfer of
volatile chemicals from shower water to air by means of tow transient mass balance models. The
calculations are outlined in Little et al. (1992). We calculated the air concentration as a function of time,
rather than a steady state approximation.
The exposure factors used were: air exchange rate shower (2.4 L/hr), air exchange rate bathroom (0.28
L/hr), shower volume (2,800 L), bathroom volume (8,100 L), water flow rate (13.7 L/min) (Little et al.
1992). These values are consistent with Kerger et al. (2000). The chemical specific parameters were
estimated using EPISUITE and the following values were used in our calculation: diffusivity in air (6.66
x 10-6 m2/sec), diffusivity in water (6.98 x 10-10 m2/sec), and unitless Henry’s law (3.59 x 10-4) (USEPA
2012).
𝐼𝑛ℎ𝑎𝑙𝑎𝑡𝑖𝑜𝑛𝑀𝐶𝐻𝑀 =
𝐶𝑎𝑖𝑟 𝑥 𝐶𝐹 𝑥 𝑡𝑒𝑣𝑒𝑛𝑡 𝑥 𝐼𝑅 𝑥 𝐸𝐹
𝐵𝑊
Where:
InhalationMCHM: Inhaled dose of MCHM during shower (mg/kg)
Cair: Concentration of MCHM in air, estimated using the Little method (1.37 µg/m3, 137 µg/m3,
424 µg/m3)
CF: Conversion factor (0.001 mg/µg)
tevent: Assumed duration of showering (0.28 hr/event)
IR: Inhalation rate of an adult (0.67 m3/hr) (USEPA, 2014)
EF: Exposure frequency (1 event/day)
BW: Adult body weight (80 kg) (USEPA, 2014)
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Toxicity of MCHM: Supplementary materials
Scenario I: Assuming the MCHM tap water concentration is the detection limit:
1.37
𝜇𝑔
𝑚𝑔
𝑚3
𝑒𝑣𝑒𝑛𝑡
𝑥0.001
𝑥
0.28
ℎ𝑟
𝑥
0.67
𝑥1
3
𝑚𝑔
𝜇𝑔
ℎ𝑟
𝑑𝑎𝑦
𝑚
= 3.21 𝑥 10−6
80 𝑘𝑔
𝑘𝑔
Scenario II: Assuming the MCHM tap water concentration is the CDC short-term health advisory:
137
𝜇𝑔
𝑚𝑔
𝑚3
𝑥0.001 𝜇𝑔 𝑥 0.28 ℎ𝑟 𝑥 0.67
𝑥 1 𝑒𝑣𝑒𝑛𝑡/𝑑𝑎𝑦
3
ℎ𝑟
𝑚
= 3.21 𝑥 10−4 𝑚𝑔/𝑘𝑔
80 𝑘𝑔
Scenario III: Assuming the MCHM tap water concentration is the highest concentration detected in
finished water:
424
𝜇𝑔
𝑚𝑔
𝑚3
𝑥0.001
𝑥
0.28
ℎ𝑟
𝑥
0.67
𝑥 1 𝑒𝑣𝑒𝑛𝑡/𝑑𝑎𝑦
𝜇𝑔
ℎ𝑟
𝑚3
= 9.94 𝑥 10−4 𝑚𝑔/𝑘𝑔
80 𝑘𝑔
Summary of Estimated Intake MCHM for the Exemplar Water Concentrations
Adult Exposure MCHM per day (assuming one bathing/showering event)
Pathway
Ingestion of tap water
Dermal contact during
bathing
Inhalation during
showering
Daily Dose
(mg/kg-day)
for 0.01 ppm
tap water
0.00031
2.52 x 10-5
Daily Dose
(mg/kg-day) for
1 ppm tap
water
0.031
0.00252
Daily Dose
(mg/kg-day)
for 3.1 ppm
tap water
0.097
0.00781
Percent
Contribution to
total Dose (%)
3.21 x 10-6
3.21 x 10-4
9.94 x 10-4
0.95
91.6
7.45
6
Toxicity of MCHM: Supplementary materials
References
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Kerger, B. D., C. E. Schmidt, and D. J. Paustenbach. 2000. Assessment of airborne exposure to
trihalomethanes from tap water in residential showers and baths. Risk Anal 20 (5):637-51.
Little, J.C. 1992. Applying the Two-Resistance Theory to Contaminant Volatilization in
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