PCDD/F levels in free range chicken eggs from north and south of Vietnam
Being lipophilic and persistent in the environment PCDD/F are able to bio-accumulate intensively (Focant et al, 2008). Poultry eggs (particularly chicken eggs) are widely used as bio-indicators of dioxin contamination and for human health risk assessment, for they are common food item, their sampling and transportation is relatively easy compared to most other biological samples (such as blood, breast milk, meat), and their fat content is appropriate for dioxin analysis. Moreover, free-range hens can easily access and ingest soil particles and soil organisms, and therefore reflect environmental levels (Chang et al., 1989, Di Gangi and Petrlik, 2005). Other pathways of soil related exposure in chickens are: inhalation of dust and skin contact (Schuler et al., 1997). In addition, it was shown that congener profiles seen in chicken eggs (as well as in liver tissue) more nearly approximate the profiles of exposure than profiles seen in adipose (Chang et al., 1989). The uptake of contaminants in soil and its carry-over to eggs depend on several factors, such as the concentration of the contaminant in the soil, bioavailability, metabolic stability, flock size, foraging behavior, time spent outdoors, and accessibility of feed (Schuler et al., 1997, De Vries et al., 2006, Kijlstra et al., 2007). Hens foraging on soil contaminated with PCDD/Fs, even at low levels (ppt), can accumulate these compounds to an unacceptable concentration.
Chicken meat and eggs are an important source of animal fat and proteins for Vietnamese. Large territories in the southern part of Vietnam were subjected to Agent Orange (AO) spraying, while northern territories were not. It is also worth-mentioning that northern part of Vietnam is generally less industrialized than southern, what can also impact dioxin levels found in chicken eggs.
The aim of the present study was to assess current contamination of free-range chicken eggs by PCDD/F in different Vietnam provinces. As a preliminary study two expeditions were organized in 2010 and 2011 to southern and northern provinces of Vietnam respectively. Only pooled samples were analyzed. As obtained results showed higher concentrations in southern part of Vietnam (Kudryavtseva et al., 2013) it was decided to conduct more thorough research in the area, this time analyzing individual eggs instead of pooled samples, in order to obtain more detailed information on PCDD/F levels in eggs, their range and variation within separate private housings.
Egg samples were collected at common Vietnamese private housings, where people live and rear animals for their own use or sometimes for sell. Also, burning trash in their backyards is very common. In 2010 chicken eggs were collected from private housings in Lao Cai province in the northern part of Vietnam and in the following provinces in southern part of Vietnam: Dong Nai, Binh Thuan, Ninh Thuan, Khanh Hoa, Dak Nong and Kon Tum. In 2011 4 provinces in northern part of Vietnam were covered: Lao Cai, Yen Bai, Phu Tho and Vihn Phuc. A total of 24 chicken egg samples consisting of 2-6 individual eggs were analyzed. In 2013 sampling was carried out only in the southern part of Vietnam (Dong Nai, Binh Thuan, NinhT huan, Khanh Hoa provinces). A total of 62 individual eggs from 14 private housings (3 to 5 eggs from each site depending on availability) were sampled and analyzed separately. Due to the lack of eggs in several housings it was not always possible in 2013 to obtain samples from exactly the same housings as in 2010. In such cases samples were obtained in the closest available housing. To our knowledge, the housings were not located in the vicinity of any special dioxin source (except for the sites near the Bien Hoa airport).
After sampling all eggs were hard boiled and frozen. Prior to extraction samples were spiked with a mixture of 13C12-labelled standards. Two extraction methods were used: pressurized liquid extraction (1:1Hexane:Ethanol) for freeze-dried samples (Klyuev et al., 2003) and (NH4)2SO4 salting-out extraction for wet samples (Shelepchikov et al., 2008). Clean-up procedure consisted of three steps: activated carbon column (AX-21), multi-layer column and aluminum oxide column (Klyuev et al., 2003). Following purification recovery standards were added. Extracts were then analyzed for 17 2,3,7,8-substituted PCDD/F using HRGC-HRMS method. Lipid content was determined gravimetrically.
Calculation of total TEQ was based on WHO-TEF2005 (Van den Berg et al., 2006) and on WHO-TEF1998 (Van den Berg et al., 1998) for comparison with other studies. In case of egg samples for values below the limit of detection (LOD) the respective LODs were used.
To assess background levels of dioxin contamination eggs from private housings in Sa Pa district Lao Cai province were chosen, for this district is located in mountainous area away from main traffic arteries and other evident dioxin sources. Mean value was 0.67 pg WHO-TEQ2005 g-1lipid (0.74 WHO-TEQ1998 g-1 lipid), which is relatively similar to the levels observed in free-range eggs from Greece and Ireland (0.37 and 0.47 pg WHO-TEQ1998 g-1lipid respectively) (Leondiadis et al., 2008; Trustos et al., 2004). For comparison, in the IPEN study the range from 0.2 to 1.2 pg WHO-TEQ1998 g-1 lipid was used as background level (Di Gangi and Petrlik, 2005).
In the southern part of Vietnam PCDD/F concentrations in chicken egg samples at 9 sites out of 14 exceeded the current EC limit for eggs and egg products (2.5 pg WHO-TEQ2005 g-1 lipid (EC, 2011)). Whereas all samples from the northern part of Vietnam were below this value. It should be noted that 2,3,7,8-TCDD contribution to the total toxicity in southern samples was generally higher than in northern samples. In 2013 elevated dioxin concentrations in home-produced eggs in southern part of Vietnam were confirmed – mean PCDD/F concentrations in eggs from 12 sites out of 14 were higher than EC limit.
To characterize Bien Hoa hot spot (location of a large US Air Force base and Agent Orange storage during the Vietnam War) eggs were collected in a private housing in Buu Long district (to the west of the airbase). PCDD/F concentration was 107.6 pg WHO-TEQ2005 g-1 lipid (108.4 g WHO-TEQ1998 g-1 lipid, 104 pg I-TEQ g-1 lipid), which is actually among the highest dioxin concentrations ever reported in chicken eggs (713 pg WHO-TEQ1998 g-1lipid, 514 pg I-TEQ g-1 lipid,126 and 122 pg WHO-TEQ1998 g-1 lipid in Belgium (Larebeke et al., 2001), Germany (Malisch et al., 1996), Egypt (Di Gangi and Petrlik, 2005) and France (Pirard et al., 2004) respectively). However, it is worth mentioning that unlike other cases the Belgian "dioxin incident" occured in not free range farms. As this housing had stopped existing by the time of our next expedition, in 2013 samples were collected in another housing in Buu Long district and in a housing in Tan Phong district (to the east of the airbase). Mean concentration found in Buu Long was 361 pg WHO-TEQ2005g-1 lipid (355 pg I-TEQ g-1 lipid) with min 302 and max 490 pg WHO-TEQ2005g-1 lipid. Concentrations in eggs from housing in Tan Phong ranged from 9.0 to 14.5 (mean value 11.1). 2,3,7,8-TCDD contribution to total TEQ amounted to 84.5 %, which is in line with a study of Hoang et al. (2014) in the same area (TCDD accounted for 61-96% of the total TEQ). Another dominant contributor was 1,2,3,7,8-PeCDD (8.4 %), while contributions of other congeners were lower than 2 % of the total TEQ.
Second highest concentration was found in housing in Ma Da logging site (16.3 pg WHO-TEQ2005 g-1lipid), with 2,3,7,8-TCDD, 1,2,3,7,8-PeCDD and 2,3,4,7,8-PeCDF being dominant contributors to TEQ (59%, 21% and 6% respectively). Because of such a high level and 2,3,7,8-TCDD domination it was decided to collect samples from one more housing in this area in 2013. Although TEQ values in both housings in 2013 were lower than in 2010 (6.7. and 4.0 pg WHO-TEQ2005g-1lipid), their profiles were quite identical. Only profiles of the samples from the 2nd housing were characterized by somewhat less contribution of 2,3,7,8-TCDD - about 40 %. It should be mentioned that Ma Da territory was subjected to AO spraying during the Vietnam war.
Total TEQs from other sites in southern part in 2010 ranged from 0.8 in Dak Nong province to 8.0 pg WHO-TEQ2005g-1 lipid in Vinh An, Vinh Cuu district, Dong Nai province. In 2013 somewhat higher levels were observed in Vinh An: mean 10.6 (range 5.7-16.8). In Tan Binh, another site in Vinh Cuu district, TEQs ranged from 3.3 to 7.9. For comparison in the study of Hoang et al. (2014), total TEQs in chicken eggs from Vinh Cuu district ranged from 3.3 to 9.7 pg WHO-TEQ2005g-1 lipid.
Among the sites investigated in 2013 9 sites were the same or closely located to those investigated in 2010. It cannot be stated whether PCDD/F concentration had significantly changed over 3 years, taking account of different sampling strategies. However congener patterns were in most cases quite similar in both studies. Rather different profiles were observed only in case of Vinh An, Dong Nai province (although samples were obtained from the same housing). In eggs sampled in 2010 2,3,7,8-TCDD, 1,2,3,7,8-PeCDD and 2,3,4,7,8-PeCDF made the main contribution with 45 %, 24 % and 12.5 % respectively. Whereas in eggs sampled in 2013 their values were 22 %, 31 % and 9.5 % respectively and 1,2,3,4,7,8-HxCDD was also one of dominant contributors with 17.5 % of total TEQ.
Almost all other samples TEQs were dominated mostly by 1,2,3,7,8-PeCDD and 2,3,4,7,8-PeCDF. For comparison, a profile found in free-range eggs from a polish farm was dominated by 2,3,4,7,8-PeCDF, 1,2,3,6,7,8-HxCDD and 1,2,3,4,6,7,8-HpCDD (J.Piskorska-Pliszczynska et al., 2014).
In all samples OCDD made the main contribution to the total PCDD/F concentration (24-88%), which is in line with other studies (Pussemier et al., 2004, Van Overmeire et al., 2009; Rawn et al., 2012, J. Piskorska-Pliszczynska et al., 2014). However, its contribution to the total toxicity did not exceed 1.5 %. In samples, collected in 2013, the fact of OCDD domination in total PCDD/F concentration (pg g-1 lipid) was confirmed in all sites except for the housing in Buu Long, Bien Hoa (Bien Hoa airbase hot spot) and one sample in Ham Tan, Binh Thuan, where 2,3,7,8-TCDD made the main contribution.
As for range of concentrations in individual eggs within a separate housing, relative standard deviations of total TEQ ranged from 6 to 53 % (mean 30.5 %). Differences in the contents may be explained by peculiarities of the hens as well as unevenly distributed dioxins in the top soil layer (J.Piskorska-Pliszczynska et al., 2014).
Dioxin levels in chicken eggs in the southern part of Vietnam are generally higher than in the northern part. 2,3,7,8-TCDD contribution in a number of southern sites is substantially higher than normally observed in background and industrially contaminated areas. As TEQs in egg samples from majority of investigated housings in southern part of Vietnam exceeded the EC limit it is not advised to use them as a foodsource. Range of concentrations in individual eggs within a separate housing is relatively small, thus a pooled sample can provide a sufficiently precise characteristic of contamination.
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PCDD/F levels in free range chicken eggs from north and south of Vietnam
Kudryavtseva A,D., Shelepchikov A.A., Brodsky E.S.
This studу concerns free range chicken eggs contamination with dioxins in Vietnam. In 2010 and 2011 years the study covered 10 provinces in southern and northern parts of Vietnam with a total of 22 pooled egg samples. PCDD/F levels ranged from 0.4 to 108 pg WHO-TEQ2005 g-1 lipid. In 2013 62 individual eggs from 14 sites in southern part of Vietnam were analyzed. Almost all samples from southern part of Vietnam exceeded the EC limit for eggs and egg products 2.5 pg WHO-TEQ2005 g-1 lipid, while none from the northern part did. Mean dioxin concentrations ranged from 1.3 to 361 pg WHO-TEQ2005 g-1 lipid. The highest concentration of 490 pg WHO-TEQ2005 g-1 lipid was observed in Buu Long near the Bien Hoa airport, which is the second highest concentration ever reported in free range chicken eggs.