Transcript Age specific estimates of hourly dust and soil ingestion

Age Specific Estimates of Hourly Dust and Soil Ingestion Rates in a
Residential Area
Johan Bierkens, Christa Cornelis, Mirja Van Holderbeke, Rudi Torfs
[email protected]
INTRODUCTION
RESULTS AND DISCUSSION
Indoor dust highly contributes to an unhealthy
indoor environment. When settled on surfaces,
it may be ingested via hand-mouth or handobject contact. When re-suspended, it may
pose a serious source of inhalation exposure.
Few studies are available on outdoor
(contaminated) soil as a source of indoor dust.
Information on the contribution of dust in total
soil&dust ingestion is often lacking. However,
in view of the large contribution of indoor
contaminants in the total exposure, this
information is essential. Therefore a
mathematical model to calculate hourly soil
and dust ingestion rates was developed which
uses estimates of daily soil&dust ingestion
rates from tracer studies, estimates of the time
spend in- and outdoors and the indoor/outdoor
ingestion ratio as input variables.
The dust ingestion rate indoor is the difference
between the total soil and dust ingestion rate
and the soil ingestion (indoor + outdoor) rate
based on estimates of tracer studies:
DIin  SItotal  TRACER
Equation 2
with:
DIin = the dust ingestion rate indoor (mg/day)
The soil ingestion rate outdoor can be derived
from the total soil and dust ingestion rate, the
time spent indoor and outdoor and the ratio
between the ingestion indoor and outdoor:
SI out


Tout

 SI total  
 Tout  f r  Tin 
Equation 3
with:
SIout = the soil ingestion rate outdoor (mg/day)
The soil ingestion rate indoor can be calculated
as the difference between the total soil
ingestion rate and the soil ingestion rate
outdoor:
SIin  TRACER SIout
Equation 4
with:
SIin = the soil ingestion rate indoor (mg/day)
The total ingestion rate of soil and dust indoor
is the sum of both ingestion rates:
I in  SIin  DIin
Equation 5
with:
Iin = soil and dust ingestion rate indoor (mg/day)
For children a mean soil ingestion (TRACER in
the equations) of 63 mg/day (based on
arithmetic mean values from literature for
children 1-6 years old) was assumed. For
adults a mean soil ingestion of 46 mg/day
(based on arithmetic mean values from
literature) was used in the calculations. The
fraction exterior soil in interior dust was set at
0.5 (assuming residences with garden) as
recommended by Cornelis and Swartjes
(2007). To determine the ratio ingestion indoor/
ingestion outdoor the default value 45/55 used
by US-EPA in the IEUBK model was
recalculated on an hourly basis. For the current
calculations the time spent outdoors and
indoors by children and adults belonging to
different age bins defined in the harmonized
method for risk assessment (Cornelis &
Swartjes, 2007) was adopted.
The approach developed here results in rather
high estimates of the hourly ingestion rate of
soil outdoors for children of 1 to 3 years old, for
15 to 21 year olds, and also for adults of 21 to
31 year in a residential setting with garden,
due to the specific time patterns in these
cases. The daily time spent outdoors is very
low, relative to the total awake time, resulting in
a low fr and hence a high soil ingestion
outdoors. It might be considered pooling the
result of the 1 to 3 year group with the 3 to 6
year group, to get a more reasonable estimate
of 39 mg/h of ingested soil outdoors.
Hourly ingestion rates (mg/h) for adults and children.
METHODOLOGY
Soil
outdoors
The total ingestion rate of soil and dust can be
split up into the intake of soil outdoor, dust
indoor and soil indoor. Bierkens and Cornelis
(2006) have developed a model that allows to
derive ingestion rate values for soil indoor and
outdoor and dust indoor from tracer study
data, and both for daily ingestion as for hourly
ingestion rates. In this model, the total dust
and soil indoor and outdoor ingestion rate can
be calculated as:
SItotal
TRACER Tout  f r  Tin 

Tout  f r  f rsoil  Tin


Equation 1
with:
SItotal = the total daily ingestion rate of soil and dust indoor
and outdoor (mg/day)
TRACER = the total daily ingestion rate of soil indoor and
outdoor (mg/day) – taken from literature
Tout = the awake time outdoor (hours/day)
Tin = the awake time indoor (hours/day)
fr = the ratio between ingestion indoor and outdoor (-)
frsoil = the fraction soil in (soil + dust) indoor (-)
Soil
indoors
Dust
indoors
Total soil
and dust
Children
1 - < 3 years
3 - < 6 years
6 - < 10 years
10 - < 15 years
15 - < 21 years
Housing with vegetable garden
78
2.1
2.1
26
2.1
2.1
20
2.0
2.0
26
1.8
1.8
49
2.8
82.2
30.2
24
29.6
2.8
54.6
Housing with garden
1 - < 3 years
3 - < 6 years
6 - < 10 years
78
26
20
2.1
2.1
2.0
2.1
2.1
2.0
82.2
30.2
24
10 - < 15 years
15 - < 21 years
26
98
1.8
2.8
1.8
2.8
29.6
103.6
Adults
Housing with vegetable garden
21 - < 31 years
31 - < 41 years
28
22
1.9
1.5
1.9
1.5
31.8
25
41 - < 51 years
51 - < 61 years
19
16
1.5
1.5
1.5
1.5
22
19
61 - < ... years
17
1.5
1.5
20
Housing with garden
21 - < 31 years
31 - < 41 years
41 - < 51 years
71
41
28
1.9
1.5
1.5
1.9
1.5
1.5
74.8
44
31
51 - < 61 years
61 - < ... years
22
28
1.5
1.5
1.5
1.5
25
31
Bierkens, J., C. Cornelis 2006. Opstellen van gebruiksafhankelijke waarden voor bodemingestie (No2006/IMS/R/387). Mol, België: VITO
Cornelis, C., F.A. Swartjes 2007. Ontwikkeling van een geharmoniseerde methodiek voor beoordeling van gezondheidsrisico's door bodemverontreiniging in de Kempenregio: VITO, Mol, Belgium and RIVM, Bilthoven, the Nederlands.
CONCLUSIONS
Hourly soil and dust ingestion rates calculated with the proposed mathematical model allow the risk assessor to predict exposure to soil- and dustborne pollutants for a particular setting in residential areas with garden or vegetable garden for different age categories more accurately, i.e. on an
hourly basis. Especially on dust these data have long been missing. However, the method cannot be used in a residential setting without garden.