User:Tnickle8/sandbox

Levels in Humans
PFOS is detected in the blood serum of almost all people in the U.S., but concentrations have been decreasing over time. In contrast, PFOS blood levels appear to be rising in China where PFOS production continues. In people, the highest exposures to PFOS in blood have been 12,830 parts per billion for occupational exposure and 656 parts per billion—or possibly 1,656 parts per billion—in a consumer. Occupationally exposed individuals may have an average level of PFOS over 1000 parts per billion, and a small segment of individuals in the upper range of the general population may be over the 91.5 parts per billion level.

... PFOS exposure occurs has been demonstrated as early as fetal development during pregnancy since PFOS can easily pass through the placenta. It has been shown that fetal exposure to PFOS is quite prevalent and PFOS has been shown to be detected in greater than 99% of umbilical cord serum samples ( https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8038605/ ). .....

PFOS has been detected in municipal wastewater and drinking water samples, worldwide, at concentrations ranging between few ng/L and some μg/L.

Health effects in humans and wildlife
.... There has been a growing body of evidence investigating the health effects of PFOS on the reproductive, developmental, liver, kidney, thyroid, and immunological effects in humans. .....

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Pregnancy Outcomes
Several studies have focused on pregnancy outcomes in infants and mothers who are exposed to PFOS during pregnancy. For developing offspring, exposure to PFOS occurs through the placenta. While the impact of PFOS compounds on fetal development continues to be an ongoing investigation, findings have demonstrated a relationship between PFOS exposure in pregnant mothers and negative birth outcomes.

There has been some evidence to suggest that ... PFOS levels in pregnant women have been associated with preeclampsia.... preterm labor and gestational diabetes  ( https://www.epa.gov/sites/default/files/2016-05/documents/pfos_hesd_final_508.pdf ). Although, the strongest association is between PFOS levels with preterm birth and preeclampsia (Gao et al., 2021, https://www.epa.gov/sites/default/files/2016-05/documents/pfos_hesd_final_508.pdf ). There has been some evidence to suggest that PFOS impairs fetal growth during pregnancy, although findings have been inconsistent ( https://www.epa.gov/sites/default/files/2016-05/documents/pfos_hesd_final_508.pdf ).

The specific physiological mechanisms behind adverse pregnancy outcomes with PFOS exposure remain unclear. One proposed cause has to do with PFOS impairment on placental blood flow (Blake & Fenton, 2020). This mechanism could help explain several of the pregnancy-related outcomes from PFOS exposure including such as intrauterine growth development, low birth weight, preterm birth labor, and preeclampsia. Additional physiological mechanisms may include disruption in inflammatory signals during pregnancy, decreased trophoblast signaling and trophoblast migration (Szilagyi et al., 2020). Additionally, PFOS exposure has been shown to be related to the downregulation genes corresponding to growth factors, pregnancy-related signal transducers, and maternal hormones (Li et al., 2016). PFOS impact on thyroid hormone regulation also has the potential to impact several birth outcomes (Ames et al., 2020; Moog et al., 2017).

Infertility
PFAS compounds such as PFOS act as an endocrine disruptor of the reproductive system ( https://www.endocrine.org/topics/edc/what-edcs-are/common-edcs/pfas ). As such, there is concern over the impact of this compound on fertility. There is some evidence to suggest that PFOS may impair fertility in both females and males. One study found that women with higher levels of PFOS and PFOA took longer to become pregnant than those with lower levels, suggesting that the chemicals may impair fertility. The impact of PFOS on male fertility is still under investigation. There have been some studies that demonstrated that PFOS is associated with a decrease in sperm count and as well as a decrease in the number of morphologically normal sperm ( https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8038605/ ). There has also been evidence to suggest that PFOS may also reduce testosterone levels. ( https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8038605/ ).

Breastfeeding and Lactation
PFOS has been measured in breastmilk and is estimated to contribute the greatest level of PFOS exposure in infants. Specifically, the duration of breastfeeding has been shown to be associated with increases in PFOS in infants. Some evidence has shown that breastmilk provides more than 94% of the PFOS exposure in infants up to 6 months old. The Agency for Toxic Substances and Disease Registry (ATSDR) concluded that breastfeeding benefits continue to outweigh potential risks associated with PFOS in breastmilk.

Thyroid Disease
Increased levels of PFOS have been shown to accumulate in thyroid gland cells and has been associated with altered thyroid hormone levels. Thyroid hormones are essential for daily functioning and are important in growth and metabolism  ( https://www.ncbi.nlm.nih.gov/books/NBK500006/ ). Appropriate levels of thyroid hormone during pregnancy are critical for a developing fetus as this hormone is involved with brain development and body growth ( https://www.ncbi.nlm.nih.gov/books/NBK500006/ ). Studies have demonstrated a relationship between PFOS exposure and thyroid dysfunction during pregnancy resulting in altered thyroid hormone levels in both the mother and the fetus ( https://www.frontiersin.org/articles/10.3389/fendo.2020.612320/full ) ( https://ehjournal.biomedcentral.com/articles/10.1186/s12940-020-00647-1 ).

Hypercholesterolemia
PFOS has been associated with increased risk of abnormal levels of cholesterol. Specifically, epidemiological studies in humans have reported an association between increased PFOS levels and the total cholesterol and low density lipoprotein (LDL) cholesterol. It remains unclear whether the changes in cholesterol are actually caused by PFOS levels in the body. The specific mechanism in humans is still largely unknown.

ADHD
Levels of PFOS in US children aged 12–15 was associated with an increased risk (60% over the interquartile range) of attention deficit hyperactivity disorder (ADHD). The importance of exposure timing during development is unclear, however, some evidence has shown that exposure to PFOS during fetal development was not associated with an increased risk for developing of ADHD later in childhood.

Chronic Kidney Disease
Serum levels of PFOS were found to be associated with increased risk of chronic kidney disease in the general US population. "This association was independent of confounders such as age, sex, race/ethnicity, body mass index, diabetes, hypertension, and serum cholesterol level." According to a 2002 study by the Environmental Directorate of the OECD "PFOS is persistent, bioaccumulative, and toxic to mammalian species."

In Wildlife
The levels observed in wild animals are considered sufficient to "alter health parameters".

PFOS affects the immune system of male mice at a blood serum concentration of 91.5 parts per billion, raising the possibility that highly exposed people and wildlife are immunocompromised. Chicken eggs dosed at 1 milligram per kilogram (or 1 part per million) of egg weight developed into juvenile chickens with an average of ~150 parts per billion in blood serum—and showed brain asymmetry and decreased immunoglobulin levels.