The effect of age on the fluoride concentration in the metacarpus of grazing sheep in New Zealand.

AIM: To determine the concentration of fluoride (F) in the metacarpi from ewes of varying age, which had been grazing pastures that had been regularly topdressed with phosphatic fertilisers, which contain F as a contaminant, for at least 30 years. METHODS: Three groups of 10 ewes aged 6-8, 18-20 and 60-72 months were selected from seven research farms with a known fertiliser history, representing the major sheep farming regions of New Zealand. Lambs were born and remained on the property. The sheep were collected and slaughtered in autumn, and the right metacarpus removed for determination of F content. Representative samples of topsoil (0-30- and 30-60-mm depths) were also collected for determination of F content. RESULTS: The total concentration of F in topsoil on the farms ranged from 161 to 712 mg/kg. The overall mean concentrations of F in metacarpi from 6-8-, 18-20- and 60-72-monthold ewes were 170 (SE 9.9), 308 (SE 13.9) and 480 (SE 28.4) mg/kg dry matter (DM), respectively. On six farms, lambs which had been exposed to limited or no ingestion of soil had the lowest concentration of F in their metacarpi. Generally, there was a curvilinear relationship between age and concentration of F in the metacarpi of sheep. On the seventh farm, the concentrations of F in the metacarpi from the 6-8- and 18-20-month-old sheep were similar but lower than those of the 60-72-month-old ewes. The area of soils on the farm where the 6-8-month-old-sheep were grazing had higher total concentrations of F in topsoil (271 mg/kg) than those soils grazed by the 18-20-month-old sheep (205 mg/kg), and this may be one reason for the elevated concentration of F in the metacarpi of the younger ewes. The concentrations of F in metacarpi, at any age, were not related to the concentration of F in topsoils. CONCLUSIONS: Many factors can influence the amounts of F in soil ingested by grazing sheep and the concentration of F in their bone. The concentration of F in the metacarpi of ewes generally increased curvilinearly with age, and the rate of accumulation of F in bone was greatest in young sheep. The potential risk of chronic fluorosis occurring in sheep grazing pastures in New Zealand is low for animals managed in a manner similar to the flocks studied, given the highest mean concentration of F was 601 mg/kg DM, observed in metacarpi from 60-72-month-old ewes, and that a concentration of at least 2,400 mg/kg DM is the threshold for chronic fluorosis.

The effect of a temporal change in ingestion rates of fluorine (F) in soil on the concentration of F in serum and bone of young sheep.

AIM: To determine the changes in concentrations of fluorine (F) in serum and bone of young sheep given a high intake of F, as F in soil, followed by a low intake of F, to simulate the varying intakes experienced by grazing sheep. METHODS: Sixty autumn-born, weaned, mixed-sex lambs were randomly divided into two groups (n=30). One group (Control) was fed a low-F (12 mg/kg dry matter; DM) lucerne/ grain diet for 345 days, while the other group (High soil-F) was fed a high-F (224 mg/kg DM) lucerne/grain diet containing 10% soil for 94 days and then a low-F diet for a further 251 days. Blood samples were collected on Days 1, 32, 94, 108, 153, 214, 280 and 345, to determine concentrations of F in serum. Groups of five or six animals from each group were killed on Days 1, 94, 153, 214, 280 and 345, to collect radii and humeri for determination of F content. The sheep were weighed at about 6-8-weekly intervals. RESULTS: Initial liveweight of the sheep was 22.1 (standard error (SE) 1.12) kg and the mean liveweight gains were 270 (SE 22.1) and 170 (SE 12.4) g/day from Days 1 to 94 and 95 to 330, respectively. The mean initial (Day 1) concentration of F in serum was 0.03 (SE 0.005) mg/L, and this changed very little for animals on the low-F diet. In sheep on the high soil-F diet, the concentration of F in serum reached 0.38 (SE 0.021) mg/L at Day 94 but after being placed on the low-F diet concentrations decreased to 0.04 (SE 0.006) mg/L after 14 days (Day 108) and then remained at about this low level for the remainder of the duration of the study. The mean concentrations of F in the humerus and radius of the lambs at Day 1 were 161 (SE 19.4) and 159 (SE 20.4) mg/kg DM, respectively, which increased to 2,784 (SE 80.6) and 1,805 (SE 51.5) mg/kg DM, respectively, at Day 94 in lambs fed the high soil-F diet, then decreased to 1,075 (SE 58.1) and 1,064 (SE 61.6) mg/kg DM at Day 153, and then progressively increased to 1,669 (SE 57.7) and 1,312 (SE 30.8) mg/kg DM at Day 345. CONCLUSIONS: The ingestion of F in soil by sheep markedly increased their concentrations of F in serum and bone, but when the soil was removed and they were fed a low-F diet, concentrations of F in serum decreased to baseline levels within 14 days while concentrations in the bone only decreased to 60-70% of the peak concentration, indicating that some of the F in bone was remobilised.

Fluoride accumulation in pasture forages and soils following long-term applications of phosphorus fertilisers.

Ingestion of soils with high fluoride (F) concentration may cause chronic fluorosis in grazing animals. Analysis of New Zealand pasture soils with long-term phosphorus (P) fertilisation histories showed that total surface soil (0-75 mm depth) F concentration increased up to 217-454 mg kg-1 with P fertiliser application. One-third to two-thirds of F applied in fertilisers resides in the top 75 mm soil depth. Pasture forage accumulation of F was low, and therefore, F intake by grazing animals through pasture consumption is expected to be much lower than F intake by soil ingestion. Ten annual applications of single superphosphate (30 and 60 kg P ha-1 year-1) to a Pallic Soil (Aeric Fragiaqualf) significantly increased total F and labile F (0.01 M CaCl2 extract) concentrations to 200 and 120 mm depths, respectively, of the 300 mm depth investigated. The mobility of F in the soil profile was similar to two other elements, P and cadmium derived from the fertiliser.

Downward movement of cadmium and phosphorus from phosphatic fertilisers in a pasture soil in New Zealand.

Total cadmium (Cd) and phosphorus (P) concentrations in a pastoral soil, amended annually for 10 years with four forms of P fertilisers, decreased with soil depth. Single superphosphate (SSP) and North Carolina phosphate rock (NCPR) which had higher Cd contents (32 and 41 mg kg(-1), respectively) produced higher total soil Cd than diammonium phosphate (DAP-10 mg kg(-1)), Jordan phosphate rock (JPR-5 mg kg(-1)) and control treatments to a depth of 120 mm. Total soil P in SSP treated plots to a depth of 120 mm and NCPR treated plots to a depth of 75 mm was also higher than the control plots. No significant fertiliser P and Cd moved below 120 mm depth. Approximately 90% of the applied Cd was recovered in the soil of which 93% remained within the top 120 mm. Plant recovery of applied Cd was 1.5-4.5%. Plant available P (Olsen P) also decreased with depth. Plant available Cd (0.01 M CaCl2 extractable Cd) was higher in the 30-75 and 75-120 mm soil depths compared to 0-30 mm soil depth. This may be due to strong adsorption of Cd by the surface soils which have a higher organic matter content and higher pH; factors which are known to increase Cd adsorption in soils