## Supplementary Data

Use of blood Mn concentration during pregnancy for model evaluation During pregnancy, it was observed that the concentration of Mn in b lood gradually increas e s compared to the pre

- conception period, reaching approximately a two
- fold gre ater level at around the end of gestation in humans (Spencer, 1999; Takser et al. , 2004) . There are severa l possible explanations for the elevat ed blood Mn . Fractional uptake of Mn during pregnancy is expected to increase due to shared absorption mechanism s in the gut with other trace elements, most notably iron, the absorption of which is greatly enhanced during pregnancy in humans (Svanberg et al. , 1975; Whittaker et al. , 1991) . The molecular basis of this competition between iron and Mn at the level of gut absorption is likely due to the broad substrate specificity of DMT

- 1 (Tallkvist et al. , 2000; Aschner and Aschner, 2005) . Cha nges in hormonal status could also be one of the reasons for the altered blood Mn concentration compared to pre

pregnancy. The alterations in calcium and bone metabolism during pregnancy imply that a potential change in Mn mobilization from the bone could also occur (Prentice, 2000) . Rothenberg et al. (1994)
re ported bloo d lead concentration showed an upward trend during the last half of pregnancy. They proposed that m obilization of lead from the bone, increased gut absorption, and increased retention could be responsible for the observed changes in blood lead level s . Alth ough more information is still needed, a similar extent of flu ctuation in blood Mn during normal menstrual cycle was reported by some researchers (Davis and Greger, 1992; Das and Chowdhury, 1997)
. Interestingly, th e M n balance measured in the late pregnancy was slightly positive similar to the findings in adult female s , with no sign of a substantial increase or decrease in fecal excretion of this element (Campbell, 1988) despite the large increase in blood Mn
. Assuming that blood Mn is still reflective of body Mn status during pregnancy, this could indicate that the b iliary ind uct ion during pregnancy may not be as responsive to the elevated blood Mn as in non

- pregnant status. At this poi nt, it is not clear whether the observed increase in blood Mn would reflect concomitant changes in the brain ofpregnant women , since the nature of th is blood Mn increase is now known
. It would be worth while to

explore how much fluctuation in brain Mn could be tolerated without causing neurological effects in women not only during pregnancy but also during normal menstrual cycles. Research of this so rt could determine to what extent variation in brain Mn should be considered normal for the risk assessment strategy of this element as suggested in Andersen et al. (Andersen et al. , 1999)
. Considering t he limited information on underlying mechanisms for increased blood Mn during pregnancy, we were reluctant to make changes in Mn absorption and excretion during pregnancy , and thus we did not attempt to fit the pregnancy model to the blood Mn data. The sam e descriptions as the adult females were used for fractional uptake and biliary excretion during pregnancy. As a result, blood Mn in the pregnant mother was under

- predicted by the current model (Table 4). It should be noted that the current description has some limitation s in predicting maternal Mn in blood and possibly in other tissues including the brain during pregnancy. Although not applied in the final form of the current model, we tested the impact of applying several plausible mechanisms that might cause the elevation of blood Mn during pregnancy on the model predictions. Tested hypotheses were changes in gut absorption and tissue mobilization of Mn during pregnancy . By incorporating a gradual increase in fractional uptake over the period of gestatio n, we were able to simulate the observed increase in blood Mn to a reasonable approximation
. At the end of pregnancy, the fraction of Mn absorbed into the body was 1.7 fold higher than the basal fractional uptake in adult females to reproduce the reported elevation of blood Mn seen throughout pregnancy, especially in the late period, in humans along with the placental Mn at the time of delivery (Spencer, 1999; Takser , et al. , 2004)
. The concurrent increase in brain Mn was about 150 to 200 % of the normal adult level in late gestation , for which, at this point, no information is available to confirm this extent of elevation
. If th ese predictions are accurate , they beg the question of how pregnant women tolerate so muc h fluctuation of Mn in brain, while neurological effects were implied to be occurring within a narrow margin of increase in blood Mn from the median value in general population (Mergler et al. , 1999)
. Albeit not as serious as neurological effects, there is some conjecture of plausible influences of this ‘naturally occurring’elevation of blood Mn on body functions (Penland and Johnson, 1993) . These authors proposed potent ial

contribution of Ca and Mn intake levels to menstrual distress including mood changes and increased pain during the premenstrual phase.

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