Effects of Chronic Manganese Exposure 

on Neurobehavior and School 

Performance in 4th Grade Students

A Pilot Study
Manganese

Neurotoxin

Adults – occupational

Adults – chronic environmental

Children

Diet vs. inhaled

USEPA reference standard - .05 um/m3

ATSDR reference standard - .04 um/m3
Marietta, Ohio

4 miles North and East of largest and 

longest active ferro-manganese alloy 

plant in the United States

Average emissions of 450,000 pounds 

per year since 1988.

University of Cincinnati air modeling 

shows Marietta exposed to an average 

of between .09 and .19 ug/m3/year
Air monitors

1 air monitor in service since 2001 

located 4 – 5 miles N-NE from emission

For the three years 2001 – 2003 avg. = 

0.23 um/m3, two monthly readings over 

1.2 um/m3

In spite of stable TRI reports, amount at 

monitor decreased to an average of just 

over .1 after 2003
Air Monitors, continued

In April, 2007, three more air monitors 

were installed, 2 across the river in WV, 

the other on the West side of Marietta

WV monitors, located 1 and 4 miles from 

emission, averaged 0.15 and 0.17um/m3 

respectively (8 months data)

Marietta monitor (4 miles) averaged 

0.1um/m3 for the eight months
Study design

Surveys and consent forms sent home 

with all 4th grade students (295 total)

68 returned (23%)

30 qualified as life-long residents

Athens, Ohio chosen as a control due to 

similar population, median income, 

ethnic diversity and school expenditure –

45 miles to the north and west
Study design continued

Surveys and consent forms sent home 

with all 4th grade students in Athens (168 

total)

36 returned (21%)

19 students matched for age (within 2 

months), gender, ethnicity, and number 

of years of parental education (within 2 

years of mother, 3 years overall)
Study design: tests

WRAT spelling test

Rapid naming

Multistep directions

Month recitation

Time

Direction

Balance

Attention
Study design: tests

Midline crossing

Santa Anna Dexterity

Visual Contrast Sensitivity (VCS)

One Hour Memory

Social Skills Rating System

4

th Grade Proficiency Tests (writing, 

reading, math, citizenship (social 

studies), and science
Results

Test Athens 

mean

Athens 

std dv.

Martta 

mean

Martta 

std dv.

Paired 

t-test p

WRAT 

spelling

18.00 7.19 12.80 5.36 0.011*

Rapid 

Naming

40.60 5.07 45.23 12.18 0.195

Multistp 

Direct

7.67 2.05 7.07 2.81 0.109

Month 

recite

1.13 1.85 0.73 1.33 0.339

Time 1.53 0.83 1.67 0.72 0.165
Results continued

Test Athens 

mean

Athens 

std dv.

Martta 

mean

Martta std 

dv.

Paired ttest p

Direction 4.60 0.63 4.47 0.99 0.353

Balance 13.74 9.15 8.64 8.44 0.005**

Midline 

crossing

34.38 6.14 41.84 18.09 0.089

Santa Ana 

Dominant

34.40 6.15 36.06 4.97 0.231

Santa Ana 

Non-dom.

30.40 5.23 33.27 4.92 0.148

One hr. 

memory

0.93 0.26 0.67 0.49 0.005**
Results- Fourth Grade Proficiency

Ohio 

Mean

Athens 

Mean

Athens 

Sample 

Mean

Athens 

Stnd. 

Dev.

Mariet. 

Mean

Mariet. 

Sample 

Mean

Mariet. 

Stnd. 

Dev.

P-value

Writ. 5.00 5.00 6.00 1.37 5.00 4.31 1.78 0.002

**

Read. 217.0 223 227.1 20.56 220 219.4 20.70 0.105

Math 214.0 225 229.2 32.18 219 220.8 34.77 0.184

Ctznship221.0 242 249.6 29.84 226 226.6 24.81 0.012

*

Sci. 211.0 228 235.4 37.37 221 214.9 43.4 0.048

*
Results- Visual Contrast Sensitivity

Spatial Frequency (Cycles/Degree)

1.5 3 6 12 18

Visual Contrast Sensitivity

20

40

80

120

140

160

Athens (N=19)

Marietta (N=19)
Shortcomings

Small sample size (19 matched pairs)

Possible sampling error

Differences between Marietta and 

Athens

Not blinded

No biological samples – does not relate 

effect to dose of Mn
Nevertheless...

Children born and raised in Marietta 

have some of the highest environmental 

exposure to Mn (.1 - .2 um/m3/year) in 

the United States

They also performed significantly worse 

on 5 of the 12 tests administered: WRAT 

Spelling, 4th Grade Proficiency, Balance, 

VCS, and Memory
Implications

Children are likely the most sensitive 

population

Very few studies have been done on the 

effects of chronic Mn exposure in 

children

Results presented here, while not proof, 

are disturbing

Study on this issue is desperately 

needed