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Lead emission decreasing around University of St. Thomas

Friday
APRIL 12, 2002
50¢ Star Tribune
NEWSPAPER OF THE TWIN CITIES
/ .
Edition
www.startribune.com

Lead emission decreasing around University of St. Thomas

By Yong Ho Kim
anonymous submission

SAINT PAUL, MN.―― Are students at University of St. Thomas (UST) more environmentally conscious than the mean of the population?

The riverbank area of St. Thomas is well-known for its natural beauty and is a favorite track for many morning runners. Thomasites enjoy of the sight in their particular way – driving BMWs down the river, and stopping at every turn.

Provided by St. Thomas Admissions Website

The riverbank green area provides a wonderful sight, worth a visit – only during summers.
Neighbors have been complaining for years about the pollution this kind of quasi-tourism leaves behind in the air, particularly the emission of unleaded gas burnouts.

The past few months, however, the visible affects arising from Lead in air in this area has decreased considerably. Less deformed babies are born at nearby hospitals. What’s going on? Two chemistry majors from Macalester College (Mac), Yang Hwa Kim and Bill James, under supervision of their Analytic Chemistry professor Keith Kuwata, decided to find it out using their analytic skills.
On the Thursday afternoon of 18th of March of 2002, Yang Haw Kim took four soil samples along the riverbank at the west of UST campus.

Provided by MapQuest (www.mapquest.com)

Star icon indicates site of sampling.

The first one (A) was taken right at the edge of the river, second (B) at the convex between the “floor” and the slope, third (C) in the middle of the slope, and fourth (D) on the top of the slope – beneath a snow-covered yard across Mississippi Blvd from UST buildings. Hiding from suspicious Thomasite eyes, he safely took the 63 bus back to Mac.

Their objective was to determinate the amount of Pb2+ found in the sampling locations.
Soil samples were massed in an analytic balance to ~2g, (2.0181, 2.0023, 2.0230, 1.9646) and were digested using concentrates of HNO3, and H2O2 and HCl.
The Atomic Absorption Spectrometer (AAS) owned by the Chemistry Department of Macalester College was used for measuring [Pb2+] of the digestion. The AAS was a Buck 200A, set at 217.0 nm wavelength and 7A, fueled by air.1

A1 A2 A3
A 0.003 0.005 0.004
B 0.020 0.019 0.017
C 0.012 0.013 0.015
D 0.006 0.010 0.012

For calibration purposes, James prepared three standard solutions of ~5, ~10 and ~20 ppm Pb2+ each.

ppm Pb2+ A1 A2 A3
5.005 0.106 0.110 0.103
10.01 0.205 0.198 0.210
20.02 0.385 0.381 0.379

Using the mean of three measurements, the least-squares method gave a slope of 0.019 and x-intercept of 0. Standard deviations of slope and x-intercepts were ignored since the standard deviations of individual samples were available.

Am Sm Calib
0.106 0.004 0.097
0.204 0.006 0.194
0.382 0.003 0.389
A=[Pb2+]ppm*0.019 (Eq.1)

obtained using least squares method in Excel
Graph of ppm Pb2+ against corrected absorbance
From Eq.1 [Pb2+]ppm can be isolated

[Pb2+]ppm = A / 0.019 (Eq.1.1)

This equation was used to calculate back the ppm [Pb2+] of the three samples.

From the mean of the sample measurements and their standard deviations, and plugging them into Eq. 1.1. we obtain the following:

Am Sm ppm
A 0.004 0.001 0.206
B 0.019 0.002 0.961
C 0.013 0.002 0.686
D 0.009 0.003 0.480

Also, the total amount of grams of Pb2+ present in the samples was calculated based in the original mass using

[Pb2+]ppm*gsample/106=g Pb2+

ppm gsample g Pb2+
A 0.206 2.0181 4.16E-07
B 0.961 2.0023 1.92E-06
C 0.686 2.0230 1.39E-06
D 0.480 1.9646 9.44E-07

“This data didn’t seem to match our predictions”, James said “because the Lead concentration was decreasing the closer we went from UST campus.”

Lead concentrations, including their uncertainties (uncertainties for ppm are obtained by multiplying %e of Absorbance with ppm), are as follows:

(A) 0.206 ± 0.052
(B) 0.961 ± 0.102

LEAD continues on A7:

  • This data just doesn’t make sense, James said.

LEAD from A1

(C) 0.686 ± 0.108
(D) 0.480 ± 0.160

Uncertainty ranges are a bit big (a mean of 21.5% of total value) but they’re not large enough to argue that the fact that distance from UST campus is loosely proportional to [Pb2+]

It can be shown that C is not significantly different from D by assuming a 50% confidence level. (Which is already a stretch)

ttable for 2 degrees of freedom and 50% is 0.816. (for 80% is 1.886)
tcalc = [(0.686-0.480)/spooled] * sqrt[(2*2)/(2+2)] = 0.206/spooled
spooled = sqrt{[0.1062*(2-1)+0.1602*(2-1)]/[2+2-2]} = 0.1365
tcalc=1.509

and 0.816 < tcalc < 1.886, therefore the two numbers are not significantly different for 50% or lower. However, for B and D

tcalc = [(0.961-0.480)/spooled] * sqrt[(2*2)/(2+2)] = 0.481/spooled
spooled = sqrt{[0.1022*(2-1)+0.1602*(2-1)]/[2+2-2]} = 0.134
tcalc=3.585
1.886 < 2.920 (90%) < tcalc, so 90% confidence level is not enough to prove that the proportional relationship among numbers could be mistaken.

“That might be true”, says James “but it is customary of the scientific community to use the 95% rather than the 90% confidence level”. And if we use the 95% confidence level, it can be shown that the values might not be different. (2.920 (90%) < tcalc < 4.303 (95%)).

UST administration reacted violently against James’ hypothesis. “Don’t you realize the very nature of the t test?” counter argues Mark Klein, president of UST Student Government (USTSG), “the adoption of a given level of confidence is entirely upon the mutual agreement of the scientific community. UST has been using the 90% since we built the north face campus.”

Kim suggested the possibility of an explanation based on the erosive power of water. “When I climbed down to collect the A samples,” he explains “water resulting from melting ice was running down the slope.”

Therefore, he says, most of the lead deposited in the top level D will gradually run down the bank carried by the melted water. That’s why the most concentrated lead sample is found in B, because water doesn’t flow from there anymore, it just sinks down the soil, while lead is left. “Sample A goes against the trend” observes James, “but it is because the river washes low points such as A all the time.”

MCSG has a plan of action if St. Thomas Lead emissions keep on “decreasing”

Walker said “immediate retaliation shall follow” if St. Thomas doesn’t stop “manipulating data to make themselves more appealing to prospective freshmen”.

However, inside sources reveal an even more cunning logic behind this decision. A MPIRG representative, who preferred to remain anonymous, said that the rage expressed by Walker is “a sign that Mac doesn’t care about environmental awareness issues anymore”

USTSG of course boasts of this as results of their efforts promoting environmental responsibility. However, most neighbors feel suspicious towards such a claim and keep using oxygen masks up to this day.

Provided by St. Thomas Admissions Website

Will USTSG choose to hit numerical advantage?

Meanwhile, tension between rival schools keeps on rising. Last night, hundreds of St. Thomas students marched eastward in Sumeet Avenue burning tiny trees and hammering bikes down. “If MCSG keeps insisting that the student’s t test certainty levels should be 95% and not 90%”, said Jake, “we’ll fight ‘till death. If for every St. Thomas student a Macalester student dies, and our quarrel goes to conclusion, there shall be no Mac in three months.”

Provided by Macalester Admissions Website

Will Macalester succumb against hordes of Thomasites invading the campus?

“Don’t even bother,” assures Kim “KUST*KMac is smaller than KACTC;” James is optimistic: “we will never reach conclusion.”.

  • Yong Ho Kim is at

ykim@macalester.edu (now at yokima@gmail.com)

Notes:
1 Detailed procedural instructions can be found at Prof. Kuwata’s homepage (www.macalester.edu/~kuwata), in the link “Lab Directions” (1/29/02) of the Chem 23: Analytic Chemistry class handouts section.

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