Aspectos éticos

Investigating PCBs in sewage sludge has been commonly undertaken, with research published from the USA, the UK, Netherlands, Italy, Switzerland, Canada, Ireland,

Greece and Spain. Much of this research was directed towards the risk posed from the land application of sewage sludge, as well as, quantifying the environmental release of PCBs in sludge and wastewaters. An important concept to be aware of in the discussion of PCBs is the different reporting styles. There are a total of 209 individual PCBs and quantification of all 209 is generally not possible or desirable. Concentrations were originally reported in terms of the commercial formulation, Arochlors™. Later

individual isomers were selected as representative of ΣPCB concentration. In this review the number of isomers included in the total sum of PCBs will be included in brackets, i.e.

ΣPCBs (X).

One of the first reports of PCBs in sludge was of six USA sludges (Bergh & Peoples, 1977). The concentrations were very high, having a mean concentration of 765 mg kg^-1 dw and ranging between 238 – 1,700 mg kg^-1 dw. PCBs were on the verge of being phase out in the USA at this time, which could account for the high concentrations.

While it is likely that these concentrations are accurate, it is possible that they are not.

West et al. (1980) was the next to report levels of PCBs in USA sludges. The levels were far lower than the earlier Bergh et al. (1977) study, with mean PCB concentration of 3.4 mg kg^-1 dw and ranging between 1.2 – 6.2 mg kg^-1 dw. Again, Mumma et al.

demonstrated that concentrations of PCBs in sludges from the USA were slightly greater than 1 mg kg^-1, with concentrations ranging from 0.15 – 3.6 mg kg^-1 dw and a mean of 1.2 mg kg^-1 dw (Mumma et al., 1984). Research out of the UK reported concentrations of up 22 mg kg^-1 dw (McIntyre & Lester, 1984) which wasn’t typical, as the mean concentrations were less than 1 mg kg^-1 in two separate UK sludge surveys (McIntyre &

Lester, 1982; McIntyre & Lester, 1984). PCBs in Netherlands sludges were in a similar range to the UK sludges: ΣPCBs (17) ranging 0.39 – 1.48 mg kg^-1 dw, mean 0.88 mg kg^-1 dw. The concentrations of sludges in the Eighties were typically in the low parts-per-million range, which was already far lower than the concentrations reported in the seventies by Bergh et al. (1977).

In the Nineties, the concentrations of PCB in sludges was declining and was often below 1 mg kg^-1 dw. For example, Italian sludges analysed in the early Nineties had PCB concentrations ranging between 210 and 1010 µg kg^-1 dw (Ottaviani et al., 1993). In a

follow up survey of digested sludge from fourteen UK WWTPs the total concentration ranged between 110 – 440 µg kg^-1 dw, mean 292 µg kg^-1 dw, which is similar to the concentrations reported by McIntrye et al. in the 1980s (Alcock & Jones, 1993). This work was followed up again in 2003 when Stevens et al. reported the concentration of ΣPCBs in fourteen UK sludges. The concentrations were similar to the studies conducted in the Nineties, as well as the Eighties: range 110 – 440 µg kg^-1 dw (Stevens et al., 2003).

The concentrations of the three most toxic coplanar PCB congeners (77, 126, 169) as well as 7 mono-and di-ortho-PCBs (PCB 8 28, 52, 101, 118, 153, 138, 180) were measured in nineteen sewage sludges from Switzerland. The sum of the seven mono- and di-ortho-PCBs, which are routinely measured as representatives of the PCB fraction, reached levels between 43 – 550 µg kg^-1 dw (Berset & Holzer, 1996). Sludges that received industrial effluents clearly showed higher PCB levels than rural ones (Berset & Holzer, 1996).

By the new millennium, the concentration of PCB in international sludges has decreased to be typically lower than 500 µg kg^-1 dw. For example, in a Canadian sludges survey of 2003 PCBs were not detected in any of the subset of 20 samples analysed at a minimum detection limit of 50 µg kg^-1 dw (Bright & Healey, 2003).

A survey of Spanish sludges reported the PCBs concentrations in 139 sludge samples from twenty WWTPs. The values found in these samples were 3 – 60 µg kg^-1 dw, median 30 µg kg^-1 dw, which was below the European recommended limit (Abad et al., 2005). Paulsrud et al. (1998) detected PCB concentrations of 17 – 100 µg kg^-1 dw with a median value of 42 µg kg^-1 dw in Norwegian sludges. Similarly, a recent study

Blanchard et al., 2004 reported PCBs concentrations ranging from 70 – 650 µg kg^-1 dw in sludge samples taken in a WWTP which drains the Paris area (France). Again PCBs in Greek sludges ranged between 185 and 765 µg kg^-1 dw and all were below the EU limit for use of sludge in agriculture (Katsoyiannis & Samara, 2004).

A summary of the concentration of PCBs in international sludges is presented within Table 5-6 showing that PCBs levels have declined since measurements were begun. The highest reported concentrations of PCBs in sludges occurred in the USA of 1,700 mg kg^-1

dw at a point in history when PCBs were being phased out. There is little variation of PCB concentrations between nations suggesting that PCB contamination was similar throughout developed countries. Presently, PCB concentrations rarely exceed 1 mg kg^-1 dw.

Table 5-6 Concentration of OCPs in international sewage sludges as reported in the scientific literature µg kg^-1 dw

Country Year

Method Analyte Range

µg kg^-1 dw

Mean Median Reference

USA 1976 GC-ECD

Arochlor 1254 <10 – 23,000 5,200 4,200 (Furr et al., 1976)

USA 1977 GC-ECD

Arochlor 1016 238,000 – 1,700,000 765,000 * (Bergh & Peoples, 1977)

Table 5-6 Concentration of OCPs in international sewage sludges as reported in the scientific literature µg kg^-1 dw

Country Year

Method Analyte Range

µg kg^-1 dw

Mean Median Reference

France 2004 HRGC-MS

ΣPCBs 70 – 650 * * (Blanchard et al.,

2004) Greece 2004

HRGC-MS

ΣPCBs 180 – 765 550 500 (Katsoyiannis &

Samara, 2004) Spain 2005

HRGC-MS

ΣPCBs (7) 3 – 60 * 30 (Abad et al., 2005)

<dl is used if the detection limit has not been supplied in the text, * no data provided