What and PCDF congeners are class 1

 

What is dioxin?

 

The World Health Organization (WHO) defines “dioxins and dioxin-like substances as a polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs) often having similar toxicity profiles and common mechanisms of action”. They are produced as by-products of industrial processes like the manufacture of chlorophenols and phenoxy herbicides, chlorine bleaching of paper pulp and smelting. They can also be generated by natural events, such as volcanic eruptions and forest fires”. Around 419 types of dioxin-related compunds have been identified and 30 of them have substantial toxicity with 2,3,7,8- tetrachlorodibenzo para dioxin (TCDD) being the most toxic of all (4). PCDD and PCDF congeners are class 1 human carcinogens since they have been shown to be associated with severe developmental and hormonal defects as well as immune suppression in animal models at low concentrations (5).

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Why worry?

Dioxins have a half-life of 7 to 11 years in human body because of their chemical stability and affinity for fats (4). They also undergo bioaccumulation in the food chain because of the same properties (6).

 

Chloracne, patchy darkening of the skin, and altered liver function are the most common side effects of short-term exposure to high concentrations of dioxins. Longer-term exposure can be highly toxic leading to cancer, immune system damages, developmental and reproductive problems and interference with hormones (4).

 

 

EPA has worked with industries to reduce the production and exposure to dioxins over the decade so the current exposure is from the dioxins that were produced in the past (6).

 

 

 

 

History

The San Jacinto River Waste Pits (SJRWP) has three pits, located on the west bank of the San Jacinto River near the Interstate -10 (I­ 10) bridge. The site was filled with paper mill waste high in polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in the 1960s and 1970s (7).

The eastern pits are partially submerged in river water and often gets completely inundated during high flows or tide events. Additionally, the pit area has subsided along with the surrounding land (8).

The site was listed as a National Priorities List of hazardous waste sites in 2008 and since then EPA started overseeing it. Champion Paper was the primary source of the waste relese at the site which is now bought by the International Paper. EPA assigned McGinnis Industrial Maintenance Corporation (a subsidiary of Waste Management) and International Paper, as the potentially responsible parties (PRPs) for the site clearance and management. Following EPA’s direction, a temporary armored cap was installed on the pits north of I-10 by the PRPs in July 2011 (9).

However, the EPA realized that the cap plan was an unreliable long-term solution and called for waste removal, soil excavation, and other remediation efforts, at the cost of $96.9 million, in 2016 which was to be paid by the PRPs. (8)DR1 .

 

Exposure and health risks associated with dioxin at the SJRWP

Though comprehensive studies on dioxins at sites surrounding the superfund site is outdated, data from a multilayer dioxin monitoring study showed the presence of dioxins  in surrounding areas connected to the SJR including the immediate area around the Superfund site itself situated under the 1–10 overpass. Sediment sampling from 2002 to 2011 from 47 different location as shown in the (fig 1) across 11 key bodies of water connected to the San Jacinto River (SJR) showed up to 17 toxic PCDD/PCDF congeners. The PCDDF/ PCDF congeners found at the highest concentrations also included 2,3,7,8 TCDD, the most toxic form of dioxins summarized below in fig 4 (10).

 

Fig. 1

Map of the San Jacinto River and Houston Ship Channel collection region from 2002 to 2011. The region highlighted in red denotes the borders of the SuperfundDR2  site. Sampling stations across the SJR discussed in this review are color coded to 11 different areas as follows: Bear Lake—pink; Superfund—aqua; Lost Lake—blue; Buffalo Bayou—yellow; Burnet Bay—light pink; Scott Bay—green; Tabbs Bay—light blue; San Jacinto Bay—red; Black Duck Bay—dark blue, Mouth of SJR—purple, Galveston Bay—orange

 

 

Fig. 4 Average TEQ for subdivided regions of the San Jacinto River system and Houston Ship Channel

 

 

In general, PCDD/PCDF TEQ seemed to decrease I concentration l based on the data available before 2011 except for the Buffalo Bayou and the Upper San Jacinto Bay (10). However data to predict the effectiveness of the armored cap in containing the dioxins at the SJRWP since 2011 after its installation are lacking (10).

 

Health concerns in the Eastern Harris County

A report from the Texas Department of State Health Services in 2015 following data analysis for an 18-year period spanning from 1995 to 2012 showed significantly high rate of brain, cervical, kidney, and rare retinoblastoma cancer were seen in Eastern Harris County especially in the three census tracts 2525, 2529, and 2533 bordering the SJR waste pits to the west, north/northeast, and east/southeast (Fig. 5). According to the report, “tract 2525 to the west, in which Buffalo Bayou acts as a natural border, was noted for elevated rates of cervical cancer were noted in tracts 2525, abnormally high rates of cervical and kidney cancer in addition to rare retinoblastoma cancer were observed in children in tract 2529 to the north, and high cases for brain cancer were observed in tract 2533 to the east/southeast had. Number of cervical cancer in adults was more than double the expected number with a total of 21 confirmed cases across both 2525 and 2529 census tracts. Brain cancer was also double the expected number in 2533 with a total 10 adult cases, kidney cancer was present at 1.5 times the expected value with 33 cases in 2529, and retinoblastoma cancer was over 16 times the expected value with 5 known cases in tract 2529” (11).

Fig. 5

Map of three census tracts identified as cancer clusters in relation to the waste pits and two representative sampling stations (10)

 

However Texas Department of State Health Services (DSHS) and Agency for Toxic Substances and Disease Registry (ATSDR) had concluded in 2013 that brain, kidney, cervical, and retinoblastoma cancer cannot be a typical carcinogenic endpoints for acute TCDD exposure with regards to the exposure around the SJR (7).

They also believed that the groundwater and surface water near the SJRWP site do not present as hazard to public health since the groundwater and surface water near the site are brackish and not used for drinking purposes, and the nearest residence being nearly ½ mile from the site, shallow groundwater contamination is less likely to be a health hazard in case contamination has occurred. Furthermore,  they also claimed that dioxins being poorly soluble in water and tightly bound to sediments, surface water contamination is less likely to pose a significant health hazard (7).

 

 

 

An addendum to the previous report by DSHS concluded that  though “the two cancers of concern, childhood retinoblastoma and glioma, appear at many times the expected rate in a few census tracts. However, there are a very small number of observed cases (five or fewer)” which makes epidemiological s environmental exposures study difficult, and there has been no scientific literatures to show association between childhood cancers and environmental exposures, and that the experts consulted didn’t see “any trends emerge in the data in terms of location, distribution, or frequency of cases that would indicate the need for additional studies to attempt to identify specific environmental causes”, concluded that would continue to count and monitor cancer statistics for Harris County in the future but would not pursue additional epidemiological study realte dto the cancer occurrence (11).

 DR1Need to find if it was approved

 DR2Discuss the legends with Elise-not sure