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Appendix 6: Soil Guideline Values

Derivation of dip-site-specific soil guideline values to protect human health

The general methodology provided in the Timber Treatment Guidelines (Ministry for the Environment and Ministry of Health 1997) and the Gasworks Guidelines (Ministry for the Environment 1997) was used to derive the indicative soil guideline values provided in section 5, which are consistent with existing New Zealand guidelines.

In contrast to previous guidelines, this guideline explicitly includes lifestyle-block land use as a typical New Zealand land use, which assumes that 50 percent of the produce consumed by residents is grown on-site (consumption of meat, milk and eggs of animals raised on-site is excluded). Previously this land use has been a subset of residential land use. The standard residential land-use category considered here assumes that 10 percent of the produce consumed by residents is grown on-site, while the remaining categories do not consider consumption of produce grown on-site.

The following five land-use categories were adopted.

  • Lifestyle block − residential property where 50 percent of vegetables consumed are assumed to be grown on-site. The consumption of products (eggs, milk, meat) from animals raised on-site is excluded and should be considered on a site-specific basis.
  • Standard residential − low-density residential property with home-grown vegetables contributing 10 percent of the total intake.
  • High-density urban residential − residential with minimum opportunity for exposure to soil; no produce consumption; includes daycare centres, kindergartens, preschools and primary schools, where no gardens are present.
  • Parks/recreation − parks, recreational open space, playing fields; includes secondary schools.
  • Commercial/industrial (unpaved) − unpaved commercial and industrial properties. Where paving is present, its integrity and likely effectiveness in reducing exposure must be considered on a site-specific basis. No consideration of the protection of plant life has been included.

The exposure scenarios considered are largely based on those provided in the Gasworks Guidelines, while the parameter values used are based on those contained in both guidelines. They are consistent with those used internationally and are also generally considered to be representative of New Zealand for the purpose of deriving generic values. However, different parameters have been used for the dermal exposure and produce consumption pathways.

Table A.3 provides a summary of the exposure parameters used for each scenario. The equations used to derive soil guideline values are provided in Cavanagh and Proffitt (2005).

Table A.3: Summary of the exposure parameters for each land-use scenario

Pathway

Lifestyle block (50% produce consumption)

Residential (10% produce consumption)

High-density residential

Parkland/ recreational

Commercial/
industrial unpaved

Exposure frequency (days/year)

350

350

350

350

240

Exposure duration - child (years)

6

6

6

6

- [Not applicable]

Exposure duration - adult (years)

24

24

24

24

20

Averaging time - non-threshold(years)

70

70

70

70

70

Body weight (kg):
  • child
15 15 15 15 - [Not applicable]
  • adult

70

70

70

70

70

Ingestion pathway

         

Soil ingestion rate (mg/day):

         
  • child
100 100 100 [Soil ingestion rates are different from the Gasworks Guidelines, to achieve consistency with the arsenic guideline values.] 50  
  • adult
25 25 25 [Soil ingestion rates are different from the Gasworks Guidelines, to achieve consistency with the arsenic guideline values.] 10 25

Produce (kg/day): [Wet weight (dry weight).]

 

 

     
  • child
0.077 (0.011) 0.077 (0.011) - [Not applicable] - [Not applicable] - [Not applicable]
  • adult
0.254 (0.034) 0.254 (0.034)      
Portion home-grown (%) 50 10      

Inhalation pathway

         

Exposure duration (hours/day)

24

24

24

5

8

Particulate concentration (μg/m3)

50

50

50

50

142

Inhalation rate (m3/day):

 

 

 

 

 

  • child
7.6 7.6 7.6 7.6 - [Not applicable]
  • adult
25 25 25 25 1.3 [m3/hour.]

Dermal pathway

         

Exposure duration (hours/day)

12

12

12

8

8

Exposed skin surface area (cm2):

 

 

 

 

 
  • child
2,625 2,625 2,625 2,625 - [Not applicable]
  • adult
4,700 4,700 4,700 4,700 4,700

Soil adherence factor (mg/cm2):

         
  • child
0.2 0.2 0.2 0.2 0.2
  • adult
0.07 0.07 0.07 0.07  

Contaminant-specific parameters used to derive soil guideline values in the current report are summarised in Table A.4, and a brief discussion is provided below.

Table A.4: Contaminant-specific parameters used to derive soil guideline values

Pathway

DDT

Dieldrin

Lindane

Tolerable daily intake (mg/kg-bw/day)

0.0005

0.0001

0.005

Background exposure (mg/kg-bw/day) [Subtracted from the TDI.]

0.000041

Dermal absorption factor

0.01

0.1

0.04

Plant uptake factor

0.136

0.41

0.41

 

The toxicological intake values provided by the World Health Organisation were generally used in the current report to provide consistency with toxicological intake values adopted by other government agencies such as the Ministry of Health, Environmental Risk Management Authority and New Zealand Food Safety Authority. With the exception of DDT, the intake values are consistent with those values used in the Drinking-water Standards for New Zealand 2005 (Ministry of Health 2005). Table A.5 provides a summary of the soil guideline values derived for individual pathways, and the final combined value.

Table A.5: Summary of soil guideline values (mg/kg) for individual pathways

Contaminant

Scenario

Soil ingestion

Dermal absorption

Produce ingestion

Combined [The combined value is calculated by taking the inverse of the sum of the inverse value of each pathway.]

∑DDTs

Rural/lifestyle

72

2,735

9.6

8.4

Standard residential

72

2,735

48

28

High-density urban residential

72

2,735

-

70

Parks/recreation

143

4,100

-

139

Commercial/industrial

1,955

15,600

-

1,740

Dieldrin

Rural/lifestyle

16

60

0.7

0.7

Standard residential

16

60

3.4

2.7

High-density urban residential

16

60

-

12

Parks/recreation

31

89

-

23

Commercial/industrial

425

339

-

190

Lindane

Rural/lifestyle

782

7,450

35

33

Standard residential

782

7,450

173

139

High-density urban residential

782

7,450

-

707

Parks/recreation

1,560

11,200

-

1,370

Commercial/industrial

> 20,000

> 20,000

-

14,180

The Ministry for the Environment holds more detailed information on the derivation of the soil guideline values for individual contaminants. This information can be provided on request.

Soil guideline values to protect on-site ecological receptors

A summary of the existing national and international soil guideline values for the protection of ecological receptors for the sheep-dip contaminants of concern are shown below.

Table A.6: Soil guideline values protective of on-site ecological receptors (mg/kg)

Country

Value name

Arsenic

DDT

Dieldrin

Lindane

Source

New Zealand

Minimal risk guideline value

12

1.8

0.002

0.006X

Cavanagh and O'Halloran 2006

xCavanagh and Booth 2003

Serious risk guideline value

22

13

0.5

2.1X

Soil limita

20

-

-

-

NZWWA 2003

Waste-screening criteriab

12, 1.2

500

8, 0.8

-

Ministry for the Environment 2004b

Australia

EIL

20

-

-

-

NEPC 1999

Canada

SQGe − residential

17

0.7

-

-

CCME 1999

Commercial/industrial

26

12

-

-

 

USA

Eco-SSL − plants

18

P

NA

-

US EPA 2005b, c, d

Invertebrates

NA

P

NA

-

Birds

43

P

0.0069

-

Mammals

46

P

0.000032

-

The Netherlands

SRCeco

40 (85c)

4d

4e

-

Lijzen et al 2001

IV

55

4d

4e

-

 

MPC

34

0.01d

0.005e

0.05

de Bruijn et al 1999

TV

29

1 × 10-4,d

5 × 10-4e

5 × 10-5

VROM 2000

EIL - ecological investigation level; SQGe - soil quality guideline environmental; Eco-SSL - ecological soil screening level; P - pending; NA − not available, insufficient data for derivation of an Eco-SSL; SRCeco − serious risk concentration ecotox; IV - intervention value; MPC - maximum permissible concentration; TV - target value.

a Allowable limits in soil to which biosolids have been applied.

b Based on protection of off-site receptors.

c Revised value (Lijzen et al 2001).

d Sum of DDT, DDD and DDE.

e Sum of aldrin, dieldrin and endrin.